How to Plan and Install Electronic Burglar Alarms 0810457342, 9780810457348

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How to plan & install Howard Herman

Covers suclitopics as • fire detection systems • photoelectric systems • radar detectors • volume detectors • automatic telephone diaters • night-viewing devices • bug-detecting devices • and much more! LYk

How

to Plan and Install

Electronic Burglar Alarms

Digitized by the Internet Archive in 2012

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How

to Plan and Install

Electronic Burglar Alarms Howard Bierman

HAYDEN

BOOK

COMPANY,

Rochelle Park, New

Jersey

INC.

Library of Congress

Cataloging in Publication Data

Bierman, Howard, date How to plan and install electronic Includes index. 1. Electronic alarm systems. I. Title. TH9737.B53 621.389'2 ISBN 0-8104-5734-2

burglar 2.

alarms.

Burglar -alarms .

76-50043

Copyright © 1977 by HAYDEN BOOK COMPANY, INC. All rights reserved. No part of this book may be reprinted, or reproduced, or utilized in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage and retrieval system, without permission in writing from the Publisher. Printed in the United States of America

PRINTING 77 78 79 80 81 82 83 84 85

YEAR

As the average citizen becomes more affluent, he invests in a house, buys color TV sets, stereos, and the like, and perhaps collects other luxury items such as antiques, rare paintings, and so on. Attracted to such opulence are an alarming number of burglars, drug addicts, and amateur "rip-off artists— all looking for a fast way to make a buck. Although it is difficult to keep up with the statistics on burglaries, it was reported that over a million homes were looted in the past year alone. Crime experts, however, claim that these figures are quite unreliable since many petty thefts are not reported, and that double the number of breakins actually reported could, in fact, be taking place. Years ago, homeowners could boast about leaving their doors unlocked for indefinite periods of time. Then crime started to mount and they were forced into installing heavy locks, steel doors, and window bars. But ingenious thieves picked these locks, cat burglars entered through skylights or basement windows, and the crime wave has continued unabated. Today, the picture is changing, somewhat, thanks to the "electronic watchdogs"— electronic systems that are guarding homes 24 hours a day. These include a variety of devices, such as photoelectric, ultrasonic, microwave, laser, and mechanical or magnetic switches. They are powered by a 1 1 5-volt ac power line and/or batteries. Installation and component costs may range from under $100 for a "do-it-yourself" job to over $2,000 for those who need sophisticated combination systems, custom-installed, to protect their valuables. A sudden fire poses an even more fearsome threat than burglaries. Over a half-million homes each year are damaged or

destroyed by fire, with thousands of lives lost in such disasters. Fire hazards can be substantially minimized with the protection of electronic security systems. They perform an invaluable service in immediately alerting homeowners to such emergencies. Fire and smoke sensors, together with burglar detection sensors, can be combined into effective burglar/fire systems. Automatic telephone dialers, included in such a system, can summon police when an unauthorized entry is attempted or alert the fire department should a fire be detected. You can install your own electronic system if you are somewhat handy with an ordinary hammer, drill, and screwdriver. Moreover, you can save hundreds of dollars if your home has a dozen or so entry points that require monitoring by switches or sensors. Installation is easy if you follow the detailed steps outlined— you can plan your own system, prepare your needed material list, purchase your material at discount electronic supply stores, install your own system, and, finally, test the working of the system. You do not have to be an engineer or electronic technician to do the right job. Just follow the installation steps described for each device, do a thorough and neat job, and, most of all, be patient. The electronic burglar/fire system offers an excellent method to enjoy a comparatively safe and normal way of living with the added comfort of knowing that your home and loved ones are protected by a reliable warning system should an emergency arise. H. Bierman New York, N. Y.

CONTENTS 1 . Electronic Security Systems: The New Watchdog Perimeter Systems Act as Electronic Fences Volume Detectors Form an Invisible Shield Triggering the False Alarm

1 2 4 6

2. Which System Is Best for You? Choosing the Best System for You "Open" or "Closed" Circuit : Which Is Better? "Hard-Wiring" vs Radio (RF) Transmission Let's Examine a Typical Wireless System Include a Fire Detection System Photoelectric Systems Are Simple Audio Detectors Listen with Giant Ears Volume Detectors Offer Blanket Protection Radar Detector Systems Are Preferable to Ultrasonics Body Heat, Weight, and Odor also Sound Alarms Reduce These False Alarms

10 12 13 22 23 24 25 32 35 38 43 45

3. A Variety of Alarm The Magnetic Switch: Window Foil Thwarts Bells and Sirens Scare Automatic Telephone

Components 47 The Basic Component 47 Attempted Breaking and Entering .... 54 Away Burglars 55 Dialers Summon Emergency Aid 58

4. Planning and Installing Your System Start with a Floor Plan or Blueprint Running Alarm System Wires throughout the House Doing a Neat Job with the Window Foil Installation of a Typical System

61 61 64 66 73

Surveillance and Eavesdropping: You May Be Bugged CCTV: Keeping an Eye on the Premises Night- Viewing Devices "See" in the Dark "Bugging" by Telephone or Wireless Detecting "Bugging" Devices

86 86 90 92 98

Glossary: Defining the Terms

101

Appendix: Suppliers and Manufacturers of Security Systems and Components

114

Index

119

1. Electronic Security The New

Watchdog

Crime is a rapidly rising business. Look at the number of locksmiths, burglar alarm installation companies and security forces listed in your classified phone book. They are overwhelming compared to the number listed a decade ago. Only a few years ago, the suburban dweller was content to read his newspaper and smirk at the growing crime rate in large cities. Now the same suburban homeowner faces a crime rate that is five times greater than that of city residents. A recent study of burglaries in a community of 100,000 indicated that one out of every forty homes was ransacked while one out of five suburban businesses was broken into. So now the concern of burglaries is shared by the urban and suburban homeowner and businessman. The need for countermeasures against thieves is obvious. But just as obvious is the swelling cost of running municipal communities, with barely enough funds to maintain an existing police staff let alone increasing manpower, equipment, and patrol cars. So the resident and businessman must seek to solve his own problem. Some prefer to ward off break-ins by super-strength locks attached to steel-reinforced doors. Such precautions are often no obstacles for criminals, who merely chop through walls or ceilings and ignore the welldefended doors. Others build fences around their property, buy trained guard dogs, and end up with a fortress that is difficult to penetrate unless the burglar can climb the fence and manage to subdue the dog. Electronic security systems offer a more effective solution. Perhaps not the perfect, fool-proof system since some professional burglars are adept at keeping up with the latest in alarm system designs, and are as capable of the same ingenuity in beating sophisticated electronic security systems as the clever electronic engineers plotting to outwit them. But electronic systems do offer a means to protect against the majority of thieves and intruders.

2

Electronic B urglar A /arms

Fig. 1-1.

EICO SS-500 burglar/fire alarm system.

Costs for electronic security systems can range from less than $100 for handy do-it-yourself installers to over $2,000 for elaborate systems installed by bonded, skilled specialists. Kits are available with accessories for intruder and fire detection for less than $200 (Fig. 1-1).

Perimeter Systems Act as Electronic Fences There are perimeter systems that operate like an electronic fence around the protected home. Anyone attempting entry through this electronic fence will set off a bell or siren. Each door and window is equipped with a special sensor that will respond electronically when the door or window is opened once the system has been armed. Often an entire home or factory is wired for a perimeter so that any and all entries are guarded by electronics: doors, windows, transoms, skylights, even walls and ceilings will signal any forced entry. Floor mats and stair treads conceal hidden switches to detect intruders (Fig. 1-2). For convenience, zoned systems may be included in the perimeter system design. In this manner, various sections of a large home or plant can be guarded with its own smaller perimeter system; all zoned areas terminate at the main electronic system control panel. If entry is at-

Electronic Security Systems: The New Watchdog

Fig. 1-2.

3

Mats on stair treads detect intruder.

tempted in any zone, the alarm sounds and a lamp lights at the control panel to pinpoint the location of the break-in. Zoned systems are convenient since they allow the owner to decide which areas are to be covered when he so desires. For example, the owner of a large estate may decide to host a large party and permit his guests to wander freely in all rooms on the main floor. Yet he may wish to keep an electronic guard for all rooms on the upper floor to protect against gate-crashers who may wander upstairs and attempt to remove valuable jewelry and cash. A further advantage of zoned systems is the ability to maintain some form of security in several zones of a system even though there is some failure in one zone, and the service technician cannot be available for the appropriate repairs within a day or two. Photoelectric systems or "electric eyes" are a variation of the perimeter system. Such devices are placed across entrances or hallways and will sound an alarm if anyone should pass and interrupt the beam between the source of light and the associated receiver (Fig. 1-3). Basically, a perimeter system is analagous to a fence, with the objective of keeping the criminal out. Should entry be attempted, the alarm will sound before the burglar steps inside the premises.

4

Electronic Burglar A larms

^2EK

Fig. 1-3.

Infrared photoelectric detectors (Design Controls).

Volume Detectors Form an Invisible Shield Other systems, such as volume or spot detectors, will respond only after entry. Such systems as ultrasonic or microwave detectors fill an area

Fig. 1-4.

Ultrasonic detector disguised as "English Language Dictionary" (3M Co.).

Electronic Security Systems: The New Watchdog

5

with invisible waves of high-frequency signals. As long as there is no motion in the protected area, the alarm is quiet. Should anyone move within the area after the system is armed, off goes the alarm. To foil the burglar, many ultrasonic detectors are designed to appear like something other than an electronic guard; a good example is 3M's Book Intruder Alarm (Fig. 1-4). Why risk a prowler entering your home before setting off the alarm? Under these circumstances, installation of a perimeter system sounds wiser, doesn't it? Perhaps so. But the perimeter system is a wired system (in most cases), and there is an expense for the labor involved. And holes must be drilled for the wires to be run from one room to another, from basement to attic; some homeowners are not too anxious to have anyone disturb their expensively decorated premises. Volume detectors, such as the ultrasonic or microwave detector, are generally self-contained (Fig. 1-5) and require no installation other than careful adjustment based on manufacturer's specific instructions.

&

Fig. 1-5.

Ultrasonic detector (Design Controls).

Well, then, why not use volume detectors and eliminate the cost and work of perimeter systems? For one, a volume detector protects a specific area, such as a door entrance or room, not an entire home. Of course, a number of volume detectors can be purchased and placed in each room if desired— but that can be costly. But the major disadvantage of all types of electronic security systems is that of false alarms. And volume detectors are more prone to false alarms than perimeter systems.

6

Electronic Burglar A larms

Triggering the False Alarm Let's assume your neighbor has purchased an elaborate electronic security system and has properly informed you that a loud siren screeching from the eaves of his home means a burglary is in progress. "If we are out and you hear the siren, notify the police immediately," they inform you. One night a week later, the siren sounds and you call the police. A short while later, you and your neighbor are both embarrassed trying to explain to the police how the neighbor's teenage son returned home from a date and forgot the alarm was set. Perhaps a week or two later, a similar incident occurs with the same embarrassing explanation. It's going to be a rare occasion when you again decide to phone for police assistance when the siren sounds. Except the next time it may occur when a burglary is actually in progress. A wire may become loose in a perimeter system hookup, and the alarm will sound when the owner arms or turns the system on resulting in a false alarm. He locates the loose wire, puts it back in its proper place and turns the system on. Minutes later, he wanders out on the porch to catch a last smoke, and the alarm goes off. Another false alarm. Again the neighbors learn to ignore his system. Many owners of expensive security systems often get out of the habit (or never get into the habit) of arming their system when they leave for the evening or go to sleep. Others prefer not to risk offending their neighbors with false alarm clamors and neglect to arm their systems. So they are as well off as others not owning a system! Volume detectors are subject to false alarms since they are triggered by any motion in the protected area. Burglars are not the only moving objects that may pass within the covered area. Pets may wander into the rooms, wind drafts may move curtains or drapes, even drafts of warm air may trigger the alarm. And the detector will be triggered if the unit moves even though no one is in the room; a detector on a flimsy table will shake when a truck passes by and the alarm will sound. Spot detectors are a third form of electronic system and are designed to protect a specific point or article such as a safe or file cabinet. Such devices allow people to move freely within an area and will only sound if the safe, for example, is touched (Fig. 1-6). Which system is best for you? It depends on your needs. For most apartment dwellers, a perimeter system with sensors on all doors and windows should be quite adequate. For owners of small homes, the basic perimeter system is generally modified to include door mats and window foil (to protect large areas of glass such as picture windows or patio doors). A large estate might combine a well-installed perimeter system with vol-

Electronic Security Systems: The New Watchdog

Fig. 1-6. Capacitance or proximity alarm guards safe.

Fig. 1-7.

A wide variety of electronic intruder alarms available from Detectron.

7

8

Electronic Burglar A farms

ume detectors at several entry points, a photoelectric system on the grounds and perhaps a spot detector guarding a hidden safe. Many manufacturers supply a diversified line of detectors and sensors for total protection (Fig. 1-7). Most homeowners agree that it is wise to include a fire protection alarm system with the burglar alarm (Fig. 1-8). Estimates generally figure about 20% extra for heat and smoke sensors added to the installation. Bells or sirens generally alert all to a burglary; a horn or loud buzzer generally warns of fire.

Fig. 1-8.

Residential burglar/fire alarm systems (Record-O-Fone).

Automatic telephone dialers are often installed as an integral part of the burglar/fire protection system (Fig. 1-9). Should a sensor be triggered, not only will a bell or siren sound, but the automatic dialer will begin sequence calls to various phone numbers and transmit prerecorded messages informing the fire or police department of the type of emergency in progress and the location. Before proceeding with the installation of a telephone dialer, check your local authorities for approval. Sometimes it is desirable to have a central-station service monitor the protected area. Specially staffed personnel are on 24-hour duty observing inputs from a large number of subscribers whose homes, stores and factories have been linked via phone lines to this one central-control point.

Electronic Security Systems: The New Watchdog

Fig. 1-9.

9

Alarm system with automatic telephone dialer (Record-O-Fone).

In the event a fire or burglary sensor is triggered at any installation, the central station may dispatch its own security force or immediately summon appropriate fire or police assistance

2. Which System Is Best for You? Alarm systems can be defined in many ways; one convenient method is to classify them according to the area to be protected by the system. Thus, an installation can be defined as spot, perimeter or volume; combinations oftwo or even all three are not uncommon when valuable merchandise or expensive homes need protection. Spot protection implies coverage of one very specific point or area. For example, a safe or a display case loaded with precious stones would require special precautions even if the building had other alarm systems. During regular business hours, entry through doors and windows would be normal and the building alarm system would not be activated. Yet the safe and display case would require constant monitoring to alert the owner should a customer or burglar attempt to remove some wares. Foil tape along the glass cases, special tamper switches, floor mats with sensitive microswitches and unique stress sensors may be combined to set the alarm off should anyone touch or come too close to the protected safe or case. Perimeter protection is the most common system in existence with any and all entrance points equipped with protective sensors. Magnetic switches in doors and windows (Fig. 2-1), foil tape on the surface of glass doors and windows (Fig. 2-2), special mats on the floor and window sills all combine in a system that will be triggered should entry be attempted at any point once the system is turned on. Factories and estates would include fences or gates with sensors mounted so as to detect intruders before they can even reach the building or home (Fig. 2-3). Volume or space systems are the most recent form of protection and are designed to detect the movement of an intruder within a given area. Space alarm systems basically fill the specified area with ultrasonic (beyond the hearing range of the human ear) waves or radio waves. Should a burglar move in this specified area, the alarm would sound. Volume systems include special time-delay arrangements (usually 20 to 30 seconds) w

Which System Is Best for You?

Fig. 2-1.

Magnet contacts for door or window

INSULATED CROSSOVER

11

installation.

FOIL

FOIL

CIRCUIT WIRE

FOIL TAKE OFF BLOCKS

Fig. 2-2.

Foil applied to a double-frame window.

12

Electronic Burglar Alarms

Fig. 2-3=

Electronic fence security system (GTE Sylvania).

to allow the resident or watchman time to turn on the alarm and then leave the protected area. After 20 seconds, the system will assume its "on" condition and be ready to detect an intruder. Such systems make use of a second time-delay arrangement to allow the owner or watchman an additional 20 to 30 seconds after he has entered the premises before the alarm sounds; he can quickly go to the system alarm switch and turn off the system before the alarm sounds. A burglar not aware of the existence of the system or location of the on/off switch would enter the protected area and unknowingly set off the alarm after the 20- to 30-second delay. Choosing the Best System for You Let's analyze how one, both, three-room apartment could be well magnetic switches at the entrance leading to the fire escape warranted the floor directly below this window

or all three systems might be used. A protected by a perimeter system using door plus all windows. If the window extra attention, a mat on the sill or on could be included.

Which System Is Best for You?

13

Now suppose a homeowner wants to protect his rather large home. He would require magnetic switches at each door and every window, on the garage door, at the roof entry and the cellar door. Such sensors, properly mounted and concealed so that a burglar could not easily bypass or defeat the system, would be adequate. Now assume the homeowner is an avid collector of gold coins. He may have a special file cabinet housing his valuable collection. It would be wise to augment his perimeter system with spot protection so that anyone who managed to enter the premises would inadvertently set off the alarm when he approached or touched the file cabinet. Now assume an installation in a small department store with a jewelry section. The perimeter and spot system would be combined as described for the previous homeowner. But now include as further backup, a volume or space detector system. Here's where the "stay behind" professional burglar gets caught. He's the specialist who somehow cleverly manages to remain hidden while the last customers and all employees leave the premises. Without space perimeter protection, he can take his time selecting his choice of merchandise and then swiftly exit. Of course, the alarm would sound as soon as he leaves, but he would be long gone before the police arrived. With a space detector system, as soon as he moved from his hiding place, the alarm would be sounded, and he would be forced to flee empty-handed. There are decided advantages when combining systems. Added protection isthe most obvious. Versatility is another. As previously described, a spot and perimeter system can be combined after business hours to protect entry to the entire area as well as coverage of a specific display case. During business hours, the perimeter system can be de-activated while spot protection is still guarding the display case.

"Open" or "Closed" Circuit:

Which Is Better? If a perimeter system is considered, an option exists in the choice of

either a "closed-circuit" or "open-circuit" system. Both systems can include telephone dialers to contact the police, photoelectric cells, window switches, and door switches. The "open-circuit" system is simpler and cheaper than the "closedcircuit" system but offers several drawbacks as described later. In the "open-circuit" system, switches of the "normally closed (NC)" type are used. This means the switch contacts are "closed" when the switch is not energized or acted upon. However, in an "open-circuit" system, the protected doors and windows are closed under security conditions, and the

14

Electronic Burglar Alarms

switches used in such systems would thus be depressed or open. Should a burglar attempt entry by opening a door or window, the associated switch would spring back to its normally closed position, disrupt the circuit and sound the alarm. In an "open-circuit" system, all switches are connected in parallel so disturbing any one switch would trigger the alarm. A basic open-circuit system is shown in Fig. 2-4. When the system is armed or the system on-off switch set to "on," no current can flow through the bell since all of the sensor switches are open. Now, should anyone attempt entry (which closes the open-circuit switch), the path for current flow would be complete, and the alarm would sound. Looks fine, but what if the burglar opens the door, quickly slips inside and then rapidly closes the door? As soon as he closes the door, the switch returns to its open-circuit position and hardly much of a noise has been made. Perhaps not enough to alert the sleeping resident. The burglar can then proceed in silence and make his exit with a minimum of disturbance.

OPEN-CIRCUIT SWITCHES BATTERY BELL

SYSTEM ON-OFF SWITCH Fig. 2-4.

Basic open-circuit perimeter system.

Now suppose the basic circuit is modified with an electromagnetic relay as shown in Fig. 2-5. A relay is a form of a switch that is activated by current flowing through its coil, thus opening or closing separate contacts contained in the relay assembly. Assume the burglar enters and closes the open-circuit switch. Current flows through the relay, energizing it, thus closing contacts A and B. At this time, current will flow through the bell circuit, sounding the alarm. Now watch what happens when the burglar quickly shuts the door. Yes, he now opens the switch and restores it to its previous condition. But the relay circuit remains completed and the alarm

Which System Is Best for You?

15

m

OPEN-CIRCUIT SWITCHES

V.

BATTERY

BELL

RELAY SYSTEM ON-OFF SWITCH

Fig. 2-5. Modified open-circuit system.

bell will continue to be powered by the battery until the on-off switch is opened or the system reset. A basic closed-circuit system is shown in Fig. 2-6. When the system is turned on, current flows through the circuit through the limiting resistor and the closed-circuit switches. However, no current flows through the bell

>: LIMITING RESISTOR

+ -

BATTERY 5 J

BELL

CLOSED> SWITCHES CIRCUIT

SYSTEM ON-OFF SWITCH

Fig. 2-6.

Basic closed-circuit perimeter system.

16

Electronic Burglar Alarms

since it is short-circuited by the normally closed switches. If entry is attempted, the short circuit across the bell will be removed, current will flow through the bell, sounding the alarm. Here again, if the burglar closes the door swiftly, the short circuit will again appear across the bell and stop it from ringing. A modified closed-circuit system is shown in Fig. 2-7.

CLOSEDCIRCUIT SENSOR SWITCHES S2 A

BELL

If

I

"TJ

i-o — 6— o- — O^-i -±- RATTFRY

I

-o — ~6 —

SYSTEM ON-OFF SWITCH SI

I

BATTERY -± 2 RELAY I

RELAY 2 ■-O

O-J RESET SWITCH S3

Fig. 2-7. Modified closed-circuit system.

When the system is turned on by an "on-off ' switch one and all sensor switches S2 are in their closed position, current flows from battery 1 through relay 1. No current flows from battery 2 through relay 2. Should an intruder open a door and thus open switch S2, relay 1 is de-energized and contact G touches H. At this time, current flows from battery 2 through relay 2, causing contact A to touch C completing the bell circuit to battery 2, thus sounding the alarm. At the same time, contact D on relay 2 touches F applying battery 2 voltage to relay 2. Now should the intruder quickly shut the door and restore relay 1 to its original position, contact G would no longer contact H. However, relay 2 has already been locked or "latched" by its own contacts D and F; thus the bell would continue ringing until the system is reset by momentarily opening the normally closed reset switch S3. In both the modified closed- and open-circuit arrangements, any attempts to tamper with the sensor switch wiring will cause the alarm bell to sound and remain on until the owner turns off the system. The relay in this arrangement latches the circuit "on" once it is energized; thus it is termed a "latching" relay.

Which System is Best for You?

17

When ordering parts for an "open-circuit" system, merely refer to manufacturers' catalogs and check off those switches and sensors that are specifically designed for such systems. Since all sensors and switches are wired in parallel, the system design and wire routing can be relatively simple. But there are some serious drawbacks to the "open-circuit" system. Examine the basic diagram shown in Fig. 2-4. Suppose, for example, that one wire from the bedroom window switch was pulled loose accidently when your wife was cleaning. Some night, with the system turned on, a burglar could enter through that particular window, and the alarm would not go off. Why? Because that particular switch circuit would remain "open" whether the window was open or closed since the circuit wiring had been disturbed. Of course, the other switches would activate the alarm if they were disturbed, but the "open-circuit" system would not sense the break in circuit wiring. A simple test circuit is usually included with an "open-circuit" alarm system to allow the owner to test the condition of the battery, the bell and the wiring to these elements. But the test circuit does not permit individual test of each sensor switch or its associated wiring, only the complete system. In a "closed-circuit" system, a small current is sent through the entire alarm circuit. Here "normally open (NO)" switches are used and are depressed or "closed" when doors and windows are protected. The small current flow is routed through a sensitive electromagnetic relay, keeping a set of electrical contacts apart from each other (Fig. 2-6). Now should an entry be attempted at a window, for example, the associated "normally open" switch would spring to its "open" position and thus interrupt current flow. The loss of current through the relay would allow the contacts to close, thereby completing the circuit connecting the battery to the alarm bell. Now let's examine the action of a "closed-circuit" system, if your wife accidently pulled a wire loose from a magnetic switch in a bedroom window. When the system is turned on, the alarm would immediately sound since the circuit is not completed and no current can flow from the battery to the electromagnetic relay. In other words, the system would immediately alert you to the fact that something is wrong— a broken wire, an open window or door or a defective switch. Step-by-step inspection of each door and window sensor and the associated wiring would soon reveal the broken wire causing the trouble. Once the defect has been found and corrected, the alarm system can again be turned on; current should now flow through the completed circuit and no alarm bell warning should sound.

18

Electronic Burglar Alarms

But the "closed-circuit" system is not infallible. A burglar could break or cut a large window or glass patio door and gain entry without opening the window or door. To prevent such entry, metallic foil is glued to large areas of the glass sections and connected through special contacts to the series-connected wires in the system. The foil is extremely thin and brittle; anyone shattering the glass would cause the foil to break and create an open circuit, thus sounding the alarm. A competent burglar has methods to overcome the "closed-circuit" system. He can locate microswitches or leaf switches on a window sill, carefully cut the glass if the window is not properly foiled and use tape to hold the switches closed as he slides the window open. Similarly, he can use a pocket compass to locate magnetic switches and use his own magnets to keep the switches closed while he opens the window. To thwart such professionals, many systems are designed and installed using a combination of "open-circuit" and "closed-circuit" arrangements. One such basic configuration is shown in Fig. 2-8. Here, even a competent burglar risks sounding the alarm if he mistakingly uses a "jumper" wire across both contacts of an "open-circuit" switch guessing incorrectly that he was dealing exclusively with a "closed-circuit" system. The combination arrangement shown in Fig. 2-8, offers additional advantages besides its ability to confuse a burglar. It is possible to combine such sensors as a doorway mat switch or a fire detector which are normally "open-circuit" devices with the more common "closed-circuit" magnetic and leaf switches.

^.BATTERY

SYSTEM ON-OFF SWITCHES Fig. 2-8.

Combined

open- and closed-circuit system.

Which System Is Best for You?

19

Relays in burglar alarm systems serve to switch battery or ac line power to the bell or siren when the sensor is triggered. Although relays are relatively simple devices, they may be affected by an accumulation of dust, dirt or oxide coating on the surface of their contacts. This buildup may result in unreliable system performance, since the alarm may not sound if proper relay contact is not made. A solid-state version of the electromagnetic relay in a burglar alarm system is the silicon-controlled rectifier or SCR. Basically, here's how this device functions. As shown in Fig. 2-9, the SCR is a three-terminal device, consisting of a cathode K, anode A, and a gate G. When the SCR is nonconducting, it behaves like an open-circuit switch; when it is driven into conduction, it behaves like a closed-circuit switch.

ANODE A

GATE CATHODE

(B)

J _

Fig. 2-9. Three-terminal silicon-controlled rectifier (SCR) (A) outline drawing and (B) schematic diagram.

A basic circuit using an SCR is shown in Fig. 2-10. The anode is connected to a positive voltage relative to the cathode. The gate is supplied a signal from the alarm circuit. Now if no signal is sent to the gate electrode, the SCR will not conduct and no current can flow from the cathode to the anode and the lamp (used in this example as the device to be energized by the SCR). As long as no signal is transmitted by the alarm circuit to the gate, the SCR stays off and the lamp remains extinguished. Should the alarm switch (SI) be closed by an intruder opening a window, a positive voltage would appear at the gate, driving the SCR into conduction and thus lighting the lamp, signaling the presence of an intruder. Once an SCR is turned on, it "latches" or remains on even if switch SI is opened and the positive voltage is removed from the gate. Thus, the lamp would remain lit even if the window was quickly closed by the thief.

20

Electronic Burglar A /arms

Fig. 2-10.

SCR circuit with lamp indicator.

The only way to reset the SCR would be to momentarily remove the positive voltage from the anode by opening the reset switch S2. Now consider replacing the lamp with an electric bell so that the bell will sound when the window switch SI is opened. A conventional bell is a self-interrupting device since it contains contacts that open and close as the striker hits the bell and then springs back. This action would prevent the SCR from remaining self-latching since anode voltage would be periodically applied and removed. To overcome this problem, a resistor R3 is wired in parallel with the bell, thus allowing an uninterrupted flow of current between SCR anode and the positive voltage supply. An additional diode D is wired across the bell to suppress excessive voltage peaks which might otherwise damage the SCR. Resistors Rl and R2 limit the current in the gate circuit. Figure 2-11 is an open-circuit perimeter system using an SCR in place of a relay. Any number of open-circuit switches (SI) can be wired in the gate circuit. As long as none of these switches are activated or closed, no positive voltage will be applied to the gate and thus the SCR will be off and no current will flow through the bell. However, should any one switch be closed, even for a moment, the gate would receive a positive voltage through Rl and the SCR could conduct or "fire" sending current through the bell, sounding the alarm.

Which System Is Best for You?

21

n

Fig. 2-1 1. Open-circuit perimeter system using SCR.

A closed-circuit variation is shown in Fig. 2-12. Here any number of closed-circuit switches (SI) can be used in series. Note that the gate terminal is connected to the cathode or ground as long as all of the closedcircuit switches remain closed. Thus the gate is not positive and the SCR does not conduct. Should an intruder open a door and open one of the switches, the gate would now be disconnected from ground and receive a positive voltage through Rl, firing the SCR, sounding the alarm. As previously noted, Rl limits gate current, diode D protects against excessive voltage peaks and R3 maintains anode current flow once the SCR is turned on.

II

R3

BELL

Rl

SI

Fig. 2-12.

SI

SI

SI

Closed-circuit alarm system using SCR.

22

Electronic Burglar A farms

"Hard-Wiring" vs Radio (RF) Transmission Once a decision has been made on whether to install a perimeter, spot or volume detector, a second decision must be made. Let's assume a perimeter system is desired. Should "hard wiring" be used to connect each of the switches or sensors at the various windows and doors? Running a complete circuit of hookup wire from one sensor to the next involves quite a bit of time and energy; particularly if the installation is neatly and properly done. Wires should be concealed to maintain proper decor in the home and to frustrate the burglar looking for easy signs of wire location. A much simpler approach to a system's installation makes use of compact, solid-state radio-frequency (RF) transmitters. The same types of sensors are used as with hard-wired installations, but each sensor is wired to its closely located particular transmitter. Now, if entry is attempted, the sensor informs the transmitter which, in turn, sends out an RF alarm signal to a receiver at the security control center. The alarm will be set off by a signal relayed not through lengthy wires but by a miniature transmitter. Such RF systems save installation time and cost, eliminate unsightly wiring and can easily be removed and installed in another home, should the owner move. But initial equipment expense is high and the system is vulnerable to interference from other transmitters. A variation of wireless alarm signal transmission uses the home or factory power line to convey the alarm signal. In this system, sensors are wired to nearby transmitters which then are plugged into ac outlets. When a sensor is triggered, it activates its transmitter which then sends its alarm signals through the ac power lines to a receiver (also plugged into the ac power line). The receiver responds to the transmitted alarm signal and sets off the bell or siren. Here again, installation is simple. But the major drawback to this arrangement lies in the local power line wiring. To operate properly and allow transmission over a reasonable distance, the ac outlets must be powered from the same power company transformer. In other words, all of the ac outlets should share the same common power line. In large apartment complexes or factories, ac power may be supplied to different sections through more than one power transformer. In such cases, a transmitter plugged into an ac outlet operating from transformer 1 would not be able to communicate with a receiver plugged into an ac outlet operated from transformer 2. It is common practice when installing or selling such an ac-line operated transmission system to test the various transmitters at the specific ac

Which System Is Best for You?

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outlets where they are intended to be installed. The receiver is likewise plugged into the ac receptacle where it will be located and then the entire system is checked out for satisfactory operation. The home-protection system uses the ac power line to carry the sensor information from any of the transmitters in the system to the receiver-alarm unit. The transmitter has terminals to accept either normally open or normally closed sensors or a combination of both. Should the transmitter be activated by any sensor detecting fire or intrusion, the transmitter will immediately generate a 50-kHz* signal, developed by a two-transistor oscillator circuit. This 50-kHz signal is coupled to the 60-Hz ac power line to communicate with the receiver.

60 Hz AC POWER LINE

£

INPUT FILTER

50 kHz AMP

OUTPUT FILTER

Fig. 2-13.

60 Hz AMP

^

DETECTOR

RELAY INTEGRATOR

ALARM

SCR

Block diagram of Heath home protection receiver.

The receiver, shown in Fig. 2-13, consists of an input filter, a 50-kHz amplifier and an output filter. The purpose of this input arrangement is to route the 50-kHz alarm signal to the receiver but to reject all other frequencies which might interfere and produce a false alarm. The filter output is then applied to a diode detector and 60-Hz amplifier to recover the trigger signal. Next an integrator circuit shapes the final trigger signal before it is applied to the SCR which drives the relay that turns on the alarm. The complexity of the system is not excessive since it keeps false alarms at a minimum.

Let's Examine a Typical Wireless System An example of a wireless system operating from the 60-Hz power line is the Heath Company's Home Protection System which can be used with a variety of sensors including burglary, fire, flood, and freeze warnings.

*Hertz (Hz) is the unit of frequency equal to 1 cycle per second.

24

Electronic Burglar Alarms

The popular magnetic switch mounted on doors and windows offer intrusion sensing. Special thermal sensors can alert the homeowner of a power loss to the food freezer, causing the temperature to rise. And a water level detector can inform a homeowner, via the alarm system, that a flooding condition is taking place in his basement due to a water pipe rupture. The Heath system depends on the ac power line for its operation; hence, a power line failure also triggers the system. This is accomplished by means of a rechargeable nickel-cadmium battery contained within the receiver that is automatically switched into the system should ac power fail. The transmitter also includes a warning signal to alert the owner if there is a break in the sensor line, if someone is tampering with the system, or if there is a component breakdown. An indicator lamp is provided on each transmitter so that it is easy to identify which transmitter has sent the warning signal with installations using a number of transmitters. The third element of the Heath system is the smoke -heat detector transmitter, which sends a warning signal in the event of smoke or fire. The obvious advantages of this remote-control system is the elimination of the cost of running wires throughout the home as well as the need to affect the appearance of the household with visible wiring.

Include a Fire Detection System To detect fire, a heat detector or thermocouple is used. The device changes its electrical resistance or changes from an open circuit to a closed circuit as temperature varies from one point to another. Most homeowners are familiar with the air conditioner or furnace thermostat that clicks or switches on or off several times per hour as the room temperature varies. Similarly, the heat detector for a fire system is an open-circuit device as long as temperature is below a preset level, either 135° or 190°F on most systems (135° sensors are used in hallways, bedrooms, etc., while 190° heat sensors are used in kitchens and furnace rooms). When heat rises above the preset level, the sensor will change to a closed-circuit condition and trigger its associated alarm circuit. Smoke can be more dangerous than fire. Unsuspecting occupants of a burning home can die of smoke inhalation long before the fire reaches their bedroom. For this reason, smoke detectors are included along with heat sensors to protect a home or office building. A basic smoke detector includes a photoelectric device to sense a change in light reaching a photo-

Which System Is Best for You?

25

cell. When smoke develops, it obscures the light reaching the photocell and the alarm circuit is triggered. Smoke detectors are usually mounted at the top of a stairway where smoke would collect. Fire detectors are generally mounted in each bedroom, in hallways and the basement, in the kitchen and in the furnace room. Mountain West Alarm Co. supplies a number of fire detectors. Their model B6-001 uses a sensor in an ion chamber combined with a circuit that closely monitors the current through the ion chamber. As combustion product particles enter the chamber due to a fire, current changes produce a circuit imbalance and the alarm sounds. Another Mountain West fire alarm system, the Alumstate, is self-contained and is conveniently attached to a wall with only two screws. This unit requires no external batteries or ac power; energy is provided by two cylinders of Freon F/12 propellant. A fusible metal plug will melt when temperature exceeds 135°F and a piercing whistle will blast for about 4 minutes. Most combination burglary/fire alarm systems use two different alarm indications to allow immediate identification of the nature of the emergency triggering the alarm. Bells or sirens generally signify burglary while horns or buzzers signal fire. Harmful gases, such as dangerous hydrocarbons produced in the early stages of fire, can be "sniffed" by the special sensor in Delta Products' Early Warning Detector. The detector has its own self-contained siren and is powered from a 115-volt ac power line. In the event of fire, smoke or gas leak, the unit sends an emergency signal warning to the Delta Products PLL computer which activates an alarm. Photoelectric Systems Are Simple Photoelectric burglar alarms are quite common because of their inherent simplicity, low price, and ease of installation. Many small shops use a photoelectric cell and a light source at the store entrance to sound a buzzer or tone each time a patron enters or leaves (Fig. 2-14). Basically, the system consists of two parts; a transmitter or source of light with a lens to direct the beam and a receiver, consisting of a photocell usually connected to a relay. When the system is put into operation, the beam of light is aimed at the photocell, and the relay contacts aFe held in an open position. The contacts from the relay are connected to the alarm bell or buzzer. As long as the light beam continues to shine on the photocell, the bell will not sound. Now if someone passes the doorway and interrupts the beam of light, the photocell suddenly senses a change in its input, and causes the relay contacts to close, sounding the alarm.

26

Electronic Burglar Alarms

Fig. 2-14.

Photoelectric burglar alarm system.

Visible light beams are not obvious to most shoppers during the day and the use of photoelectric arrangements to alert the shopkeeper to the entry of a customer by the sound of a soft tone or buzzer is quite acceptable. However, for burglar alarm purposes, the simple photoelectric system is too easy to spot at night and even easier to defeat. All a burglar has to do is locate the light source, merely scan to find where the photocell is located and simply shine a flashlight toward the photocell as he passes through the light beam directed from the system's light source. The alarm will not sound since the photocell will not detect a disturbance in the arrival of a light beam. Some systems attempt to reduce the problem by inserting ultraviolet or infrared filters between the light source and its lens; but experienced burglars can't be fooled that easily. More sophisticated systems use a transmitter that has a beam of light modulated or forced to flicker at a very specific rate (Fig. 2-15). The receiver's photocell circuit is modified to sense not merely the presence of a light beam but the presence of a precisely flickering beam. Now should a burglar attempt to bypass the system by simply shining his flashlight at the photocell, the alarm would sound. A variation of the photoelectric burglar alarm employs a sensitive light meter adjusted to the normal room brightness level. If the room is normally dark, such as a jewelry shop vault, the light level would be extremely low. Now should a burglar enter and turn on a light or use his flashlight, the alarm would be triggered. Similarly, if a room is normally lit

Which System Is Best for You? LENS

LIGHT BEAM TRANSMITTER AND MODULATOR

fl

27

t a

MODULATED LIGHT BEAM PHASE DETECTOR

Fig. 2-15.

Block diagram of a modulated

RELAY

ALARM

photoelectric system.

when no one is on the premises (such as a display showroom), any burglar entering would cause a shadow reducing the light level, thus setting off the alarm. A simple photoelectric system consists of a single light source and its associated receiver. A light beam is focused on a photocell which generates a small voltage due to the input from the light source. This voltage is amplified at the receiver and keeps the contacts of a relay (connected to the alarm bell) open, when an intruder breaks the light beam, the relay contacts close and the bell sounds. This arrangement can cover up to 200 feet in a straight line assuming there are no obstructions to the light due to dust or fog. Now if it is desired to monitor an area where the light must be bent, the solution is simple. Mirrors are rigidly mounted at appropriate points, and are carefully adjusted so that the light beam covers a given distance, hits the mirror, is directed to a second or even third mirror and then is exactly directed to the receiver or photocell unit. Such modifications with mirrors greatly extend the utility of the photoelectric system (Fig. 2-16). Proper attention must be given to proper mounting and aiming of each mirror to efficiently beam the source of light around corners and building obstacles. Precautions must be taken so that employees or customers cannot accidently bump into the mirrors and upset system performance. Photoelectric systems are generally considered less susceptible to false alarms than most types of burglar alarms and offer wide area protection for relatively low cost. By cleverly arranging mirrors, a criss-cross pattern can be set up, making intruder movement easier to detect.

28

Electronic Burglar Alarms

Fig. 2-16.

Mirrors extend coverage of photoelectric system.

As previously noted, the disadvantage of photoelectric systems is due to the ability of an intruder to spot the beam and thus locate the transmitter. To confuse the burglar, photoelectric devices are supplied for recessed mounting in walls, are installed with criss-crossing beams and mirrors and units are mounted at different height levels. The use of multiple mirrors confuse the location of the beam path as well as extending intrusion coverage. For full effectiveness, a photoelectric beam should be invisible to the naked eye; this is accomplished by the use of an infrared or ultraviolet filter placed in front of the lens assembly. False alarms can be as common with photoelectric systems as with other systems. With outdoor photoelectric installations, smog or fog may

Which System Is Best for You?

29

prevent the beam from reaching the receiver, thus triggering the alarm. In heavy industrial areas, the beam may be blocked by dust or grime collecting on the surface of the light source lens or receiver lens. And it's not unusual for employees in a hurry to inadvertently leave cartons or boxes in the paths between the photoelectric cell and the receiver, thus triggering the alarm when the system is turned on. An inexpensive photoelectric system is the Archer Photoelectric Relay System (Fig. 2-17). The two units, the transmitter or illuminator and the receiver, are mounted so that the light beam between them cover the doorway or entry being supervised.

Fig. 2-17.

Archer photoelectric receiver.

Alignment of the beam is critical since the receiver includes an aperture plate to minimize the light input from any sources other than the transmitter. If the transmitted beam passes through the aperture plate, (Fig. 2-18) at an angle rather than directly, less light will hit the photocell detector. Both the transmitter and receiver should be securely mounted so that vibrations will not cause false alarms. Make sure the receiver is not planned to be located where bright artificial or sunlight can enter its lens; try to use the shady or dark side of the room. As a further precaution, shield the lens with a homemade tube of cardboard taped to the front of the lens.

30

Electronic Burglar Alarms PHOTOELECTRIC CELL

LIGHT BEAM FROM TRANSMITTER

POORLY ALIGNED Fig. 2-18.

Properly and improperly aligned photoelectric beam.

The Archer system does not house any bell or siren; instead the receiver has a 115-volt ac outlet on the back panel to which any 1 15-volt ac bell or siren can be connected (provided it draws less than 0.3 ampere). A new, state-of-the-art component, the low-power laser diode, has brought improved reliability to photoelectric systems. Capable of being powered by batteries, gallium arsenide infrared devices offer an additional bonus of small size— making ultra miniature, easy-to-conceal light sources a reality. Low-power laser systems, using gallium arsenide diodes, can cover a range of about 50 feet. Longer range laser systems are currently available, for indoor and outdoor applications, which can extend coverage to over 1,000 feet. Although laser systems are less affected by fog, snow, and rain than incandescent lamp systems, they also will be triggered should heavy dust or fog block the beam from the receiver. A semiconductor laser intrusion detection system, manufactured by Data Optics Corp., is called the "Louie D Laser." This all solid-state invisible beam system is designed primarily for outdoor use. Louie is a small, infrared laser beam system including transmitter, repeater and receiving stations. A pulsed infrared signal is generated, sent to a repeater station,

Which System Is Best for You?

31

re-transmitted to the next repeater, and so forth. The final station at the end of the perimeter to be protected accepts the passed-along signal. Should the infrared signal be interrupted at any point, the alarm would be triggered. The system is similar in principle to the photoelectric version previously described. Although this is a laser system, danger of eye damage is remote since the system's infrared emission is claimed to be less than 100 times lower than the Surgeon General's published specifications. Special circuits within the system recognize disturbances from small birds or falling leaves and will not trigger the alarm; large objects, such as a vehicle or human will set off the system. Large areas can be covered since repeater stations can be separated by as much as 1 ,000 feet with reliable performance. Louie is encased in a steel pipe 6 inches in diameter with a plastic top (Fig. 2-19). The housing is designed to look like an innocent "bumpstand" found in parking lots. To eliminate false alarms caused by movement of repeater stations due to heavy traffic or vibration, Louie units are embedded in 1 cubic yard of cement for stability. Alignment of the trans-

Fig. 2-19.

Laser intrusion detection system (LOUIE

D).

32

Electronic Burglar Alarms

mitter and repeater stations are performed with a portable infrared receiver supplied with each system. Simple thumbscrew adjustments allow exact horizontal and vertical alignment and a special meter indicates the optimum setting to receive the laser beam. A perimeter photoelectric alarm system depends on the interruption of a light beam to trigger an alarm. Another photoelectric system, the ambient light detection system, operates on a different principle. Here, the special light detector measures the light level in the area to be protected which is illuminated when the system is on. Typical examples are jewelry shops with lights left on at night so that police patrol cars can quickly spot anyone within the premises after hours. The system monitors the light level and, should an intruder enter, the resulting shadows cast would change the light level and set off the alarm. Audio Detectors Listen with Giant Ears An audio detection system in its simplest form can be considered as a giant ear listening for the slightest sound in the area to be protected. And burglars do make noise as they enter and loot a home or a plant. A block diagram of a typical audio intrusion alarm system is shown in Fig. 2-20. The audio detectors, actually sensitive microphones, pick up all sounds in the protected area and route them to the control panel. Sensitivity adjustments at the control panel permit sufficient amplification

SPEAKER

► CONTROL PANEL WITH AMPLIFIER

SPEAKER #2

SCHMITT TRIGGER

TRIGGER OUTPUT

— wv

SPEAKER #3

SENSITIVITY CONTROL Fig. 2-20.

Basic audio intrusion alarm system.

to hear faint sounds without the penalty of excessive false alarms. A special circuit, called a Schmitt trigger, is included to prevent the alarm from sounding until the sound level exceeds a preset volume; thus, where

Which System Is Best for You?

33

applications require alarm signaling at the slightest hint of an intruder such a system is ideal. However, there are applications for audio intrusion systems where brief intervals of non-repetitive sounds can occur and where it is desirable for the system not to react. Only when a series of repetitive sounds, such as an intruder's steady movements, takes place is it desirable for the alarm to trigger. Under such requirements, a sound-averaging circuit (Fig. 2-21) is included within the audio intrusion system design. The amplified sound signals are applied to a diode rectifier which develops an average value of the total audio input across capacitor C. Brief bursts of sound would produce very slight changes across C and thus the average value would not exceed the preset level. Should a repetitive series of sound signals be applied to the diode, the average voltage across C would rise and trigger the alarm.

DIODE CONTROL PANEL WITH AMPLIFIER

Fig. 2-21.

T X

TRIGGER OUTPUT

Sound averaging circuit.

Still another improvement in audio intrusion system is the soundcancellation circuit (Fig. 2-22). One amplifier is placed in the area to be protected and a second similar-type amplifier is placed outside the area. Samples of the sound picked up by both are fed to the cancellation circuit. Each rectifier diode produces a dc voltage proportional to the audio sounds routed to it. Thus, a burst of thunder would deliver almost identical sound levels at each rectifier, producing fairly equal voltage outputs from each. The voltage outputs are connected in opposing polarities to the trigger circuit input; thus, if both dc voltages are about equal, there would be a slight trigger output, insufficient to sound the alarm. Now should an intruder move within the protected area or open drawers or make any noise, some significant rectifier output would be developed. The same sound level would not be developed at the outside amplifier and its rectifier would not develop a canceling dc voltage. At this time, the trigger voltage or difference between both rectifier outputs would be sufficient to sound the alarm. Audio-detection systems are not recommended in areas where heavy machinery or traffic exist during hours when protection is desired. Nor are

34

Electronic Burglar Alarms kl INSIDE AMPLIFIER

tD-

i

.DIODE "2

>