A1 11 03091 458

Sher, Alvin H/Selectlon and application QC100 .U57 NO.480-, 14, 1979 C.I NBS-PUB

NBS SPECIAL PUBLICATION 480-14

Law Enforcement

Equipment Technology

Selection and Application

Guide to

COMMERCIAL INTRUSION

ALARM SYSTEMS
ACKNOWLEDGMENTS

This guide was prepared by the Law Enforcement Standards Laboratory of the National Bureau of Standards under the direction of Lawrence K. Eliason, Manager,

Security Systems Program, and Jacob J. Diamond, Chief of LESL. Its preparation was sponsored by the National Institute of Law Enforcement and Criminal Justice, Lester D. Shubin, Standards Program Manager.
r Selection and

Application Guide

to Commercial

Intrusion Alarm

Systems

NBS Special

Publication

480-14

by

Dr. A. H. Sher

Gerard N. Stenbakken

Center for Electronics and

Electrical Engineering

National Bureau of Standards

and the

Law Enforcement Standards Laboratory

Center for Consumer Product Technology

National Bureau of Standards

Washington, D C. 20234

prepared for National Institute of Law Enforcement

and Criminal Justice

Law Enforcement Assistance Administration

U.S. Department of Justice

Washington, D.C. 20531

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Luther H. Hodges, Jr., Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued August 1979

^^St OF
Library of Congress Cataloging in Publication Data

Sher, Alvin H. Selection and application guide to commercial intrusion alarm

systems.

(NBS special publication ; 480-14)

Supt. of Docs, no.: C 13.10:480-14

I. Burglar-alarms—Handbooks, manuals, etc. I. Stenbakken, Gerard N., joint author. II. Law Enforcement Standards Laboratory. III. National Institute of Law Enforcement and Criminal

Justice. IV. Title. V. Series: United States. National Bureau of Standards. Special publication ; 480-14. QC100.U57no.480-14n"H9739] 602'1s 78-21624

[621.389'21

National Bureau of Standards

Special Publication 480-14

Nat Bur Stand (U S ), Spec Publ 480-14,- 40 pages CODEN XNBSAV

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1979

For sale by the Superintendent of Documents

U S Government Printing Office, Washington, D C 20402

(Order by SD Catalog No C13 10 480-14) Stock No 003-003-02098-2 (Add 25 percent additional for other than U S. mailing).
CONTENTS

Foreword v Introduction 1 Basic Considerations 2 Economics 2 The Threat 3 Related Protection 5 False Alarms i The Types of Protection 8

Point Protection 9

Perimeter Protection 9 Area Protection 10

Holdup Protection ii The Sensors 13 Switch Sensors 13 Pressure Mats 14

Metallic Foil 15

Wire Screens 15

Microwave Motion Detectors 15

Ultrasonic Motion Detectors 18

Infrared Motion Detectors 19

Infrared Photoelectric Sensors 20

Sound Sensors 21 Vibration Sensors 22

Capacitance Sensors 22

System Design Considerations 22

The Floor Plan 23

Control Units 24

Tamper Protection 26

Installation and Operational Considerations 27

Environmental Factors 27

Sensor Installation Factors 28

After the Installation 30

Sounding the Alarm 31

Local Alarm System 31

Central Station System 32

Automatic Telephone Dialer 32

Direct Connect System 34

Getting Your Money's Worth 35

Table 1 . Applications of intrusion alarm sensors 12 Table 2. Comparison of intrusion sensors 16-17

Table 3. Relative effectiveness of protection systems 34

iii

The Law Enforcement Standards Laboratory (LESL) of the National Bureau of Standards (NBS)

furnishes technical support to the National Institute of Law Enforcement and Criminal Justice

(NILECJ) program to strengthen law enforcement and criminal justice in the United States. LESL's function is to conduct research that will assist law enforcement and criminal justice

I agencies in the selection and procurement of quality equipment.

LESL is: (1) Subjecting existing equipment to laboratory testing and evaluation and (2)

j conducting research leading to the development of several series of documents, including

national voluntary equipment standards, user guides, and technical reports.

' This document is a law enforcement equipment guide developed by LESL under the

sponsorship of NILECJ. Additional guides as well as other documents are being issued under

the LESL program in the areas of protective equipment, communications equipment, security

I systems, weapons, emergency equipment, investigative aids, vehicles and clothing.

Technical comments and suggestions concerning this guide are invited from all interested

i parties. They may be addressed to the authors or to the Law Enforcement Standards

Laboratory, National Bureau of Standards, Washington, D.C. 20234.

Jacob J. Diamond

Chief, Law Enforcement

Standards Laboratory

INTRODUCTION

Crimes against businesses, small and large, are a commonplace occurrence and, regrettably,

security has become essential in the operation

of any business. With the increase in burglary, more and more businesses are turning to alarm

systems for increased protection. The selection

of a suitable alarm system is not a simple

matter. You are faced with a wide and possibly

confusing array of equipment and services. For

guidance, you could: a) Read the numerous excellent textbooks on intrusion alarm systems—if you have the time; b) utilize the services of consultants in the field—if the size of your busi- ness warrants it; c) rely solely upon the recommendations of alarm system dealers and

installers—who may have only a specific

product line or type of equipment to offer; or d)

study the innumerable articles in the popular

trade press—which may not give you enough in- formation for your specific needs. This guide is intended to provide an alternate means for you

to gain a general understanding of intrusion

alarm systems and their potential use in your

business.

The factors which determine the requirements

of an individual alarm system and the questions

which must be answered when selecting a system include:

• The threat—What is to be protected

against?

• The type of protection—What

methods are available?

• The types of sensors—What should

be detected?

• The method of alarm transmission

How is the signal sent and who will respond?

The purpose of this guide is to familiarize you

with:

• the types of protection that intrusion

alarm systems can provide,

• the manner in which they operate and

• the characteristics of the various

system components as they relate to different applications.

The basic considerations that determine your in- dividual needs are discussed in general terms,

thus enabling you to more effectively deal with

and understand the services of the many

reputable alarm system companies that are ready to serve your needs.

The Law Enforcement Standards Laboratory

(LESL) is continuing to develop performance

standards for intrusion alarm components.

Equipment that meets the requirements of these individual standards will provide reliable performance with a minimum of false alarm susceptibility. In addition, LESL has prepared a number of guides and reports concerning

security equipment and systems that you will find to be useful companion documents to this guide*.

An intrusion alarm may sometimes serve to deter a would-be intruder. However, the primary

function of the system is to signal the presence

of the intruder. An intrusion alarm system is only

part of the overall protection needed; many

large businesses will supplement them with

guards and other security personnel, and even

the smallest will have a locked door. In addition,

it is important for you to recognize that the

successful operation of a system depends upon

not only the system equipment but also upon its proper installation, maintenance, and use.

"A list of all current LESL publications is available upon request from the Law Enforcement Standards Laboratory, U.S. Department of Commerce, National Bureau of Standards, Wastiington, D.C. 20234.

1
When you are deciding whiether to install an intrusion alarm system, cost cannot be the sole basis for your

decision. BASIC CONSIDERATIONS

Economics

As a businessman, you must consider the

economic aspects of your decision as to whether or not to install an intrusion alarm

system, since the acquisition and operation of the system will undoubtedly be reflected in your

overhead. However, an intrusion alarm system

has safety as well as economic aspects, and

cost cannot be the sole criterion upon which

your decision is made. You may wish to install an intrusion alarm primarily for the peace of mind that it affords you or your employees.

Intrusion alarm systems have been

demonstrated to be effective. In a typical study,

the intruder apprehension rate for protected

premises was six times that for unprotected

premises. Obviously, the chances of recovering

your property are proportional to the apprehen-i

sion rate, particularly if the intruder is taken intO j custody in or near your place of business. Ini addition, the actual dollar value of losses from a

business protected by an intrusion alarm hasi

been found to be significantly less than that of a

business not protected by an alarm system. The

potential deterrent value should not be
overlooked either. It is not uncommon for a

burglar to avoid businesses that have intrusion

alarm systems.

The choice between a local alarm system,

which signals an alarm only at the protected

premises, and a remote alarm system, which

transmits the alarm signal to the police or a

central station, will be a major factor in the

operating cost. The local alarm system, least expensive, is suitable for use if the primary

object of the alarm is to scare the intruder away

from the premises. If the objective of the

system is apprehension, a remote alarm should

be employed.

Large retail businesses or industrial firms may

choose to install an intrusion alarm system that transmits all alarm signals to a central location

staffed by its own guards or security personnel.

Such systems, referred to as proprietary

systems, are obviously expensive to operate

and can usually be justified only for large firms.

The economic aspects of installing an intrusion

alarm system are also influenced by insurance

considerations. In many instances, insurance

rates are lower if the business has an intrusion

alarm system. It is not uncommon for an

insurance company to refuse to issue a policy

to a high-risk establishment that does not have

an intrusion alarm system.

If your business is located in a city or region

classified by the Department of Housing and

Urban Development (HUD) as a high-crime

area, you should investigate your eligibility for HUD anti-crime insurance. Policies issued under

this program are Federally subsidized to provide

rates significantly lower than those of normal

commercial insurance. It is mandatory, however,

that the insured premises have an intrusion

alarm system.

Depending upon the physical size of your busi- ness premises and the complexity of the

intrusion alarm system that is installed, you will be faced with installation costs ranging from

hundreds to thousands of dollars. In addition,

service fees could range from 50 to several

hundred dollars per month. Service fees vary

considerably from one locality to another. When

' such factors as insurance rates and safety are

properly accounted for, only you can determine

if your potential property loss justifies the

expense.

The Threat

Common crimes against businesses are

burglary, arson, vandalism, and holdups. These

crimes have as a common element the unauthorized presence in an establishment of one or more individuals, usually after normal business

hours. Entry into the premises may be

accomplished by force from the outside or by

hiding inside before closing time. Generally, a

large portion of those who commit such crimes

are unskilled juveniles. Normally they have little education, training, or criminal expertise and

select targets where special skills, planning, and

training are not required to gain entry.

The potential threat to a place of business

depends upon many factors. The location (highcrime area, isolated area, shopping center, etc.) of the business is a primary factor. It has been

found that the incidence of burglary, robbery,

and theft is highest in the inner city, less in suburban areas, and lowest in rural areas. The

continued expansion of shopping centers into suburban and rural areas, however, has resulted

in rapidly increasing crime rates in areas outside

the central cities. The type of business will also

affect the probability that it will be attacked.

Leading targets for theft include jewelry, liquor,

clothing, and drugs. Establishments that

frequently have large amounts of cash on hand,

such as banks, supermarkets, discount stores,

drug/variety stores, and gasoline stations are

also frequent targets. Your local law enforcement agency, or a review of its records, can

often provide you with information as to the

types of businesses that are most frequently

attacked in your area.

The threat to your business may well encompass more than the loss of merchandise

or the proceeds from sales. The malicious

burglar, the vandal, or the arsonist may destroy

or remove important business records, resulting

in a loss of far more than the stolen cash or

3
merchandise. In addition, damage to the

building and its contents may prevent you from

conducting normal business for extended

periods of time until repairs are made and new

stock is obtained.

The time you devote to defining the potential

threat to your business will be time well spent,

for you are more likely to select an intrusion

alarm system that fully meets your needs. You

are also much less likely to purchase a system

that is more complex and expensive than you

need.

VANDALISM & ARSON

4
LOCATION

Related Protection

Although an intrusion alarm can serve to frighten an intruder away from your business, it

will not always do so. You may still suffer a loss, even though a smaller one than if you did not have that protection. Therefore, it is in your best

Interest to take additional measures to protect

your business, since the intrusion alarm is only one element of a security system.

The first and most fundamental measure is physical protection. It is quite possible, if your

business is in a low- to moderate-crime area, and not of a high-risk nature, that the installa- tion of door assemblies which will resist the

forced entry attempts of unskilled and semiskilled burglars (in combination with suitable

windows which will also resist such attacks) will provide adequate protection without the need

for an intrusion alarm system. The Law

Enforcement Standards Laboratory has

prepared guides and standards for the physical

security of doors and windows which you may

find useful.

BUSINESS

FACTORS

DETERMINING

THREAT

The manner in which doors and windows are

installed is critical to their ability to act as

physical barriers to an individual attempting to break in. The installation of doors and windows

is also important with respect to intrusion alarm

systems, for if they are loose fitting, certain

types of alarm switches installed upon them will produce frequent false alarms.

There are many other measures, not requiring a

major investment, that you can take to augment

an intrusion alarm system. Most are a matter of

good security procedures. Remove all cash

from cash registers at night. Leave the register

CASH ON HAND

5
1. INTRUSION-PROOF WINDOWS

Z INTRUSION-PROOF DOORS

a WINDOWS CLEAR (allows police or passerby to see in)

4. CASH REGISTER DRAWER (with no money) OPEN & LIGHTED

5. LIGHTS, INSIDE & OUT, ON

Since an intrusion alarm system is only one element of a security system, it is in your own best interest to take additional measures to protect your business.
drawer open with the tray visible (a light

directed on it is a good idea) so that a would-be

intruder can see from the outside that he will get no cash if he breaks in. Leave some lights on and keep sales banners in the windows to a minimum so that the police patrol can see into the building from the street.

It is also a good idea to provide lights that

illuminate doorways, particularly rear entrances. Do not park trucks so close to the building that

they could be used as hiding places or as step

ladders to second floor windows. The list is endless. Needless to say, you should remember

to lock the door when you leave, and turn on

the alarm.

The police departments of most cities and

counties have community crime prevention

units. These units will be pleased to visit your

business and provide a security survey of your

premises at no cost to you. They will help you

to identify your vulnerabilities and provide many

simple common-sense suggestions that can

help to improve your overall security.

False Alarms

One of the most important problems associated

with business intrusion alarm systems is the

high incidence of false alarms. More than nine

out of ten alarm signals are false alarms, with no evidence of actual or attempted forced entry.

A continued high rate of false alarms from your

equipment could cause the police to place a low

priority on response to your alarm, since they

would take it for granted that it was just another

false alarm. Many local jurisdictions are

seriously concerned over the time and

resources wasted on officers responding to

false alarms. As a result, some have enacted

ordinances that permit fines to be levied against

businesses that allow their intrusion alarm

systems to signal an excessive number of false alarms.

False alarms are also a problem with local alarms. A local alarm system that frequently

sounds false alarms quickly becomes a

nuisance to adjoining businesses, and the

chances of a neighboring businessman calling

the police to investigate an alarm are greatly

reduced.

There are numerous causes of false alarms. In some instances the false alarm is the result of malfunctioning equipment. In other cases the

false alarm originates in the signal transmission

line. It is also true that some false alarms are in reality alarms that have been set off intentionally by a sophisticated intruder who is testing your alarm system for possible future entry or is attempting to undermine faith in your

system. The improper use or installation of many types of alarm sensors can also cause

false alarms.

The statistics that have been collected,

however, tend to support the belief that the

largest single source of false alarms is the

improper operation of the system. If the system

is turned on with a door or a window open, the sensor will transmit a false alarm. If you enter your store at an odd hour without first notifying

the police or central station (assuming you have

a remote alarm), you will transmit a false alarm.

CAUSES OF FALSE ALARMS

EQUIPMENT MALFUNCTION

IMPROPER INSTALLATION

IMPROPEI OPERATION

The largest single source of false alarms is improper operation. Buy a system you and your employees can operate properly, thus preventing

false alarms.

Once you install an alarm system, it will be your

responsibility to insure that you and your

employees operate it so as to avoid false alarms. When you discuss your alarm system

needs with an installer, keep the false alarm

problem in mind and try to select a system that

you feel you and your employees can control

properly. You should also study your premises

to become aware of those factors that could cause certain alarm sensors to transmit a false alarm. For example, some sensors will transmit an alarm signal in response to a flickering

7
fluorescent light that is located nearby, while

others will transmit an alarm signal in response

to a ringing telephone bell. You should be aware of such problems, for if a sensor is installed in a business environment that

includes a source of some ^ype of stimulus to which it is sensitive, it can be expected to generate false alarms and limit the

effectiveness of your system.

THE TYPES OF PROTECTION

All intrusion alarm systems, from the simplest to the most complex, consist of three fundamental

elements or components: a sensor which

detects the action or presence of an intruder; a

control unit that turns the system on and off, receives the signal from the sensor, processes

the signal, and transmits the actual alarm signal;

and a device to summon assistance in response

to the alarm. Obviously, the system must

provide a means of transmitting information

between each of the functional elements. The

complexity of each element varies significantly,

depending upon the system.

The sensor and control unit components can be

assembled into a variety of configurations to provide four basic types of protection:

• point, spot, or object

• perimeter, or linear

• area, space, or volume

• holdup

The types of protection that you select depend

upon the threat to your business. Any or all of the basic types of protection can be combined

to make up the sensor/control unit subsystem.

If you have the idea that it would be possible to combine the four types of protection in literally a hundred different ways for a single

establishment, you are absolutely right. The

design of an intrusion alarm system is further complicated because in many cases there are

several different types of sensors from which to choose. Of course, there are many manufacturers of sensors and components, each with

products containing features that distinguish his products from his competitors'. For this reason, you can expect that no two alarm installers will propose to install exactly the same system. You

can, however, take comfort in the fact that the

general approach to protection will be similar,

leaving you to judge the advantages or disadvantages of only a few features.

All intrusion alarm systems consist of three fundamental elements: a sensor which detects the action or pres- ence of an intruder; a control unit which turns the system on and off, receives the signal from the sensor, processes the signal, and transmits the actual alarm signal; and an alarm which summons assistance in re- sponse to the alarm signal.

8

I
In many cases, the alternatives offered by

different alarm installers will be a consequence

of individual sources of supply. In every case, the reputable alarm company will make its rec- ommendation based upon experience with a

specific sensor or item of equipment, and

should know how well it can be expected to perform in your application. Do not hesitate to ask for the names of other businesses that

have systems like the one proposed for your

business. Chances are that the individual will be

glad to discuss the performance of his intrusion

alarm system and alert you to any problems that

have been experienced with it.

Point Protection

As the name implies, point protection is used to detect the action or presence of an intruder at only a single location. This type of protection,

also referred to as spot or object protection,

may be employed alone in certain limited situation, but is most often used as a part of a larger

system. Point protection can provide additional

security for certain obvious targets, such as

safes, files, vaults, jewelry counters, or other

items of high value. In a sense, point protection

is a backup system to insure the detection of an

attempt to steal specific items should an

intruder gain access to your premises without

being detected. Examples of the sensors used

for point protection are capacitance proximity sensors, which make metal objects such as file cabinets sensitive to the approach of an

intruder, and contact vibration sensors, which

detect the movement of an object.

Point protection is frequently used to protect

valuable objects of art at all times, including

normal business hours, and can also be used

during normal business hours to protect against

shoplifting. In the latter case, the alarm signal

must be directed to on-site guards or security

personnel, rather than to the police.

Sensors used for point protection detect the action or presence of an intruder at only one single lo- cation.

Perimeter Protection

Perimeter protection may well be the most

expensive as well as one of the most practical

types to install. Sensors are used to detect the

action or presence of an intruder at all vulnerable building access points such as doors,

windows, skylights, etc. This type of system

provides early detection of an attempted or successful intrusion and increases the likelihood

of apprehension. Although perimeter protection

is sometimes used as the only type of protection, it is often supplemented by point or area

protection. Perimeter protection generally uses

switch sensors (magnetic, mechanical, or mercury) and metallic foil. The switches cause

an alarm to be transmitted when the door or window is opened, and the metallic foil causes an alarm to be transmitted when it is broken.

While switch sensors can be installed so as to be concealed, they are often mounted in plain

view, to make it obvious that the business has an alarm system. The exposed perimeter

system may serve to deter the inexperienced

intruder, but it may also make it easier for the

experienced burglar to counteract the sensors

1,

9
and gain entry. Pressure mats, which cause an

alarm when stepped on by an intruder, can be

concealed under a carpet in front of doors or windows to provide perimeter protection. Such

protection can also be furnished by infrared photoelectric sensors that signal an alarm when an

intruder interrupts the beam.

The major disadvantage to the use of a perimeter protection system alone is that it offers no

protection against persons who remain hidden

inside the premises until after closing. Under

these circumstances the intruder is free to burglarize or vandalize a seemingly protected

establishment, signaling his presence only when

he leaves the building. Obviously, the chances

of apprehending the intruder are greatly

reduced in this instance.

Sensors used for perimeter protection detect the

action of an intruder at any vulnerable access point (sucfi as a door, window, sl<yiigfit, etc.).

Sensors used for area protection detect tfie pres- ence of an intruder witfiin a selected area.

Area Protection

Area protection, whether used alone or in conjunction with a perimeter system, is used to detect the presence of an intruder anywhere

within a selected area. This type of protection is also referred to as space or volume protection

because the sensors respond to intruders

anywhere within their field of view. With some

types of sensors, the detection zone is such

that there is no entry point that can be used by

the intruder without his being detected. The

major consideration when using area protection

alone is the choice of the proper area to be

protected and the protection pattern of the sensor to be used. Area protection usually serves as a backup to perimeter protection

systems by detecting the presence of the "staybehind" burglar or the intruder who gains entry

without triggering the perimeter alarm.

A variety of sensors can be used to provide area protection. Commonly employed are ultra- sonic, microwave, and infrared motion sensors. The extra expense involved in using area protection in addition to perimeter protection can be

justified if the value of the property to be

protected is high enough, if the premises to be

10
protected are highly vulnerable to perimeter

entry, or if the threat includes the probability of

attack from hidden intruders.

Holdup Protection

A holdup alarm system is a separate circuit or subsystem of an intrusion alarm system that is active during normal working hours and consists

of one or more manually actuated switches.

Because the holdup alarm is actuated by an indi- vidual on the scene, judgment is required in its use.

During a holdup, you or your employees are confronted by an armed individual who is clearly a threat to life. Hence, holdup alarms are designed so that their actuation is not obvious

to the robber. In this instance, the alarm signal

is always transmitted to a remote location, such

as a police station, with no attempt to sound an

alarm at the protected premises. The armed

intruder is normally in an agitated state of mind,

and his reactions are difficult to predict. If he

sees or suspects that an alarm has been transmitted, he could flee, or retaliate by injuring or

killing any or all persons present.

Holdup devices should be selected to permit

actuation with a minimum chance of detection.

For example, a money clip is useful, since it permits the employee to actuate the- alarm by

the very action required to satisfy the demands

of the robber—removing money from the cash

drawer. Holdup switches should also be

available at other locations, such as in a nearby

office, to enable an individual outside the

robber's view to actuate the alarm. If the size of

your business warrants guards, security

personnel, or trained individuals capable of

providing assistance during a potential holdup

situation, you might also consider the installa- tion of a suspicion alarm system that an employee would actuate with an alarm button if the actions of an individual seemed to be

improper. Such alarms are internal, and alert security personnel that it is necessary to observe the behavior of individuals on the

premises and to be prepared to respond should an attempted robbery occur.

Holdup switches should be designed so that they cannot easily be actuated by accident.

Holdup alarms receive high priority response

from law enforcement personnel, who must assume that the lives of the personnel within

the premises are being threatened. There is always the possibility of an accidental discharge

of a firearm when an officer enters the premises

prepared to defend the victims and himself.

A holdup device is a manually actuated switch set off by an employee during a holdup.

Many intrusion alarm systems that include

holdup protection also incorporate surveillance cameras to record evidence for purposes of apprehension and legal action. They are usually

controlled by the holdup alarm and are automatically turned on by the alarm signal. Their use in conjunction with a suspicion button is very

desirable, for that permits photographs to be

taken of a suspect prior to the commission of the crime. The additional precrime photographs

are usually as useful as, and sometimes more

useful than, those taken during the crime. The

use of surveillance equipment is discussed in detail in the LESL Guide, "Selection and

Application of Fixed Surveillance Cameras."

11
In some instances, the use of holdup switches

at fixed locations is not very practical. The indi- vidual who operates a small business, perhaps

as a sole proprietor, might constantly move

about the premises making it difficult to provide

fixed holdup switches at all possible working

locations. For this reason portable holdup

switches, sometimes referred to as personal

panic buttons, are becoming increasingly

popular. These devices are basically small radio

transmitters that can be carried in a pocket and

actuated in an inconspicuous manner, should

the businessman be threatened. The radio

signal is received by the control unit of the

intrusion alarm system and an alarm signal is transmitted just as if the alarm were wired

directly into the control unit. Some businessmen also use the portable

holdup switch for additional protection outside

their business establishments. For example, a businessman might install a receiver on the

exterior of his building, so that when he leaves

after the close of business, with the proceeds

for the day, he can actuate the holdup alarm if he is attacked at any point between the building

and his car in the parking lot.

TABLE 1. APPLICATIONS OF INTRUSION ALARM SENSORS

SENSOR POINT PERIMETER AREA

DRY CONTACT SWITCHES • o

MAGNETIC SWITCHES ® o

MERCURY SWITCHES • o

METALLIC FOIL e

WIRE SCREENS •

TRIPWIRE o o

PRESSURE MATS • 0

PRESSURE RIBBONS • e

PRESSURE WAFERS • o o

ACOUSTIC SENSORS o o •

ULTRASONIC MOTION SENSORS o o •

MICROWAVE MOTION SENSORS o ® •

PHOTOELECTRIC SENSORS:

PASSIVE

ACTIVE • o • o • o

CAPACITANCE SENSORS • ®

VIBRATION SENSORS •

INFRARED MOTION SENSORS o ®

# GOOD APPLICATION

® LIMITED APPLICATION

O NOT APPLICABLE

12
THE SENSORS

Selecting the proper sensors for an intrusion

alarm system is somewhat complicated. In most

cases, it will be possible to use any of several

different types of sensors for the same general

type of protection. In addition to the variety of sensors available, there are literally hundreds of companies that manufacture these devices.

There are differences between sensors manufactured by various companies and options to the basic designs are also offered, thus

providing a wide range of choice. Table 1 lists the sensors that are commonly used for each of the basic types of protection: point, perimeter,

and area.

The sensors of an alarm system are electronic

or electromagnetic devices that act as a replacement for a human observer or as a supplement to human observation. For example,

when an intruder opens a door, a switch sensor can be used to detect that it has been

opened—an action that would be obvious if you were watching the door. In this instance, the

method of detection is extremely simple—

a

switch actuation. Modern technology, however,

has developed sensors that use complex

detection mechanisms. Sophisticated sensors

are designed to "see" and signal an alarm in response to a specific stimulus or source that is considered to result from the action or presence

of an intruder (movement, body temperature,

footsteps, etc.). It must be remembered that sensors lack human judgment; when a sensor

detects that which it is designed to detect, it will signal an alarm. Thus, motion sensors will respond to animals as though they were human

intruders.

The manner in which the commonly used types

of intrusion alarm sensors operate is discussed

in the paragraphs that follow. Because of

i differences between various manufacturers'

products, the comments may not be universally

applicable.

Switch Sensors

The switch sensor is undoubtedly the most

frequently used intrusion alarm sensor. Switches incorporate electrical contacts that

make or break an electrical circuit in response

to physical movement. They are used in perimeter protection systems to detect the opening of doors and windows, and can be used as a part

of a shoplifting alarm as well as in holdup alarm

systems. You will find that most alarm installers refer to switch sensors as "contacts," and will often describe the proposed system as using a

contact on this door, or that window, etc.

The dry contact switch is a mechanical switch

similar to a light switch; several different designs are used. A plunger switch is designed

to be installed in a door or window jamb, and

operates like the switch that turns on the

interior lights when a car door is opened. Others

have small levers that are displaced by the

movement of the door or window to actuate the

contacts.

Nearly all switches used in holdup systems are mechanical switches. The money clip is a

switch in which a bill is inserted between springactuated contacts. When the teller takes the bill from the switch, the contacts close and the

alarm is sent. It is also possible that the thief himself can unwittingly sound the alarm, for the

money clip is hidden below a stack of bills. The

switches that an individual can actuate in case

of a holdup include a foot rail, which is operated

by placing one's foot under a rail and applying

pressure with the toes in an upward manner,

and hand operated switches. Those intended

for hand actuation should incorporate two

buttons that must be pushed simultaneously. All holdup switches should be designed to make

accidental actuation difficult. A trip switch is a mechanical switch designed so

that the contacts close when a small plug is removed from the body of the switch. In one

application the switch is positioned on a wall,

perhaps in a corridor, slightly above the floor. A

thin wire is attached to the switch plug and

stretched to a fixed point on the opposite wall. If an intruder walks into the wire, the plug is pulled out and the alarm is sounded. Trip switches are

also used on overhead doors, such as garage

doors.

13
(b)

•

Switch sensors have electrical contacts that make

or break an electrical circuit in response to a physical movement; they are usually used for pe- rimeter protection. This illustration shows three types of switch sensors: (a) magnetic switch, (b)

trip switch, and (c) mercury switch.

Intrusion alarm systems often use magnetic

switch sensors. Like any electrical switch,

magnetic switches can be obtained with either

normally open or normally closed contacts. Most intrusion alarm systems use the normally

closed type of switch regardless of whether it is mechanically or magnetically actuated.

The magnetic switch consists of two

components, each contained in a separate

housing. The switch is a pair of contacts that

will open or close when subjected to a magnetic

field. A separate magnet is mounted near the

switch to set the contacts to the normal

position. The magnet is mounted on the

moveable member of the item that is being

protected, such as a door or a window sash.

When it moves away from the switch the

contacts are actuated.

Since the switch contacts are held in their normal position by a magnetic field, it is possible to place a strong magnet near the

switch and thus prevent the contacts from

actuating when the switch magnet is moved

away. For this reason, a second type of magnetic switch, the balanced magnetic switch,

has been developed. This employs two

magnets with fields that interact to produce a

net field surrounding the switch contacts. The

balance of this net field is so critical that if it is disturbed by placing a non-system magnet near

the switch, the contacts will be actuated to signal an alarm.

Mercury switches, which the installer might call

"tilt switches," are used, as an example, to detect the movement of a transom. The

mercury Switch consists of contacts within a

sealed unit containing a small pool of mercury.

When the switch is tilted, or pivoted in a vertical plane, the mercury rolls between or away from

the contacts to either complete or open an

electrical circuit.

Pressure Mats

Pressure mat switches are basically mechanical

switches. You have probably encountered them

in your local grocery or department store, where

they are frequently used to automatically open

the doors as you approach. In intrusion alarms.

14
the pressure mat is most frequently used as a backup system, e.g., to detect an individual

stepping on the floor below a window through

which entry has been gained without causing

the perimeter system to alarm. Pressure mat

switches are also used as "traps" because they can be hidden under the carpet in front of a

likely target such as a valuable appliance, on

stairs, and in corridors which one would expect an intruder to use.

Metallic foil (a) breaks when the glass is broken;

this triggers an alarm. Pressure mats (b) respond

to pressure; they cause an alarm when stepped

upon. Concealed wire screens or grids (c) respond

to forced entry through walls, ceilings, doors, etc.

Miniature pressure mat switches are also

available for use in shoplifting alarm circuits. These switches are placed under objects of value and will cause an alarm if the protected

item is picked up.

Pressure mats are versatile sensors. Although

normally designed to actuate in response to a

weight of 7 kg (15 pounds) it is possible to obtain them with either higher or lower sensitivity. They are made in a large variety of sizes,

ranging from approximately 1 centimeter (less

than 1 /2 inch) to over a meter (several feet) in width, and in almost any length you might

desire.

Metallic Foil

Metallic foil, one of the simplest intrusion alarm

sensors, is commonly attached to glass to detect breakage. When the glass is broken the

foil also breaks and an alarm is signaled. While

metallic foil is most often used on display

windows, it is also used in doors with glass

glazing and on display cases containing

valuable merchandise.

Metallic foil can be easily damaged by routine

housekeeping activities such as cleaning.

Therefore, it is normally covered with a thin coat

of shellac or varnish after it has been attached

to the glass surface with adhesive.

Wire Screens

Wire screens or grids are sometimes used in intrusion alarm systems. This is a closely

spaced pattern of thin electrical wires, usually

forming a grid pattern 10 to 15 centimeters (4 to 6 inches) square. Such a grid can be used to detect forced entry through walls, ceiling, doors,

etc. The wire can also be incorporated into the

mesh of a normal window screen. When a wire

is broken an alarm is sounded, just as with

metallic foil on a window.

When a wire screen or grid is used, it is most

often covered with wallpaper, building material, or some other material, both to conceal it and

to protect it from being broken by normal housekeeping.

Microwave Motion Detectors

Microwave motion detectors are used to sense

the presence of an intruder within a volume of space or an area. These devices transmit a high

frequency electric field that is monitored by a

receiving antenna. The frequency of the electric

field changes when reflected from a moving

object, and an electronic processor circuit compares the transmitted frequency with that which is received, signaling an alarm when a change in frequency is detected.

15
TABLE 2. COMPARE

j SENSOR

DRY CONTACT MECHANICAL

SWITCHES

MAGNETIC

SWITCHES

MERCURY

SWITCHES

METALLIC FOIL WIRE SCREENS TRIP WIRES

PRESSURE

PRESSURE R PRESSURE Ij

APPLICATIONS DOORS. WINDOWS,

GATES, TRANSOMS,

HATCHES, ETC , USUALLY FOR

PERIMETER

PROTECTION,

DOORS, WINDOWS,

GATES, TRANSOMS,

HATCHES, ETC , USUALLY FOR

PERIMETER

PROTECTION.

(SAME COMMENTS

AS FOR MAGNETIC

SWITCHES APPLY. APPLICATION IS USUALLY FOR ACCESS

POINTS THAT HAVE

COVERS THAT

OPEN WITH CHANGING

VERTICAL ANGLE. THUS THESE SWITCHES OPERATE WHEN TILTED BEYOND A CERTAIN

POINT!

SHOW WINDOWS.

OFFICE WINDOWS.

GLASS DOORS. DRY WALL BOARD.

ETC . USUALLY FOR

PERIMETER PRO- TECTION.

ACCESS POINTS NOT

SUBJECT TO EVERY DAY USE. USUALLY

FOR PERIMETER

PROTECTION.

ENTRY WAYS SUCH

AS TO CORRIDORS OR IN DOORWAYS

FOR PERIMETER

PROTECTION.

SMALL AREAS DOORWAYS. UNDER SPEC OBJECTS FOf POINT PROTi t

ADVANTAGES LOW COST. RELATIVELY

RESISTANT TO ENVIRONMENTAL EF- FECTS. RELATIVELY IMMUNE TO EFFECTS

OF WEAR. LOW COST

EASILY REPAIRED.

VISIBILITY SERVES

AS DETERRENT.

LOW DEGREE OF MAINTENANCE. LOW VISIBILTIY FOR ATTRACTIVE

APPEARANCE.

LOW COST. LOW COST. I'i LOW DEGREE [J MAINTENAN A

ADAPTABLE r:| VARIETY OF jl AND SIZES. |i

DISADVANTAGES LOW RELIABILITY LOW SENSITIVITY SUBJECT TO ENVIRON MENTAL EFFECTS

HIGH INSTALLATION

COST.

BECAUSE OF MOUNTING

POSITION. MAY BE SUBJECT TO DAMAGE

IN SOME APPLICATIONS. HIGH INSTALLATION

COST.

VULNERABLE TO DAMAGE BOTH IN TENTIONAL AND

THROUGH DAY-TO DAY USE.

MUST BE REPLACED AFTER PENETRATION

TO RESTORE

PROTECTION.

MUST BE REMOVED TO ALLOW NORMAL

ACCESS. THEN

REPLACED TO RESTORE PROTECTION.

SUBJECT TO 1 ll

IN PATH OF l.V TRAFFIC. SUBJECT TO

OF HUMIDIl I.I STANDING I

RESISTANCE TO

DEFEAT

LOW. BALANCED TYPE MORE RESISTANT TO COMPROMISE THAN SINGLE MAGNET

TYPES.

LOW. MODERATE FOR CON

CEALEO TYPES LOW IF DETECTED BY

INTRUDER.

RELATIVELY! ONLY IF CC. OR PRESEN KNOWN TOFALSE ALARM

SUSCEPTIBILITY

HIGH IF DOOR OR WINDOW HAS LARGE AMOUNT OF PLAY, LOW IF TIGHT.HIGH IF DOOR OR WINDOW HAS LARGE AMOUNT OF PLAY. LOW IF TIGHT.

HIGH DUE TO

EFFECTS OF ENVIRONMENT.

LOW TO MODERATE LOW IF BUILDING

IS SOLID SUBJECT TOI MENTAL CO

1
NTRUSION SENSORS

)' ACOUSTIC

i SENSORS

;l€A PROTECTION

h ENCLOSED

: ACES (ROOMS.

ilRULTS, ETC.).

ISITIVE.

J USE EXIST. INTERCOM

STEMS, AFFECTED BY

R MOVEMENT.

iECTIVE AGAINST

Itay-behinds."

\{ >T BE USED IN

IiIaBLE NOISE VIRONMENT

K lERE BACKGROUND

!| VEL IS LOW.

'H IF PROPERLY

ITALLED.

BE HIGH BUT bUCED USING

DITIONAL CAN

-LATION MICROlONE.

ULTRASONIC MOTION SENSORS

AREA PROTECTION

OF SMALL EN CLOSED SPACES

IROOMS. COR

RIDORS, ETC.

I

USUALLY NOT

DETECTABLE BY

INTRUDEREFFECTIVE AGAINST "STAY

BEHINDS." EASY PHYSICAL

INSTALLATION.

SEVERELY AFFECTED

BY ENVIRONMENTAL

FACTORS. AIR TURBULENCE AND

MOTION. RATTLING

DOORS. JANGLING

KEYS. BLOWING

DRAPERIES. VIBRATIONS. LOUD

NOISES. ETC ESSENTIALLY LINE OF-SIGHT OPERATION: LARGE OBJECTS COULD

SHIELD INTRUDER. MAY NOT DETECT EX- TREME RATES OF MOVEMENT (VERY SLOW OR VERY FASTIHIGH IF PROPERLY

INSTALLED.

CAN BE HIGH UNLESS ENVIRONMENTAL

FACTORS ARE CON

SIDERED BEFORE

APPLICATIONMICROWAVE

MOTION SENSORS

AREA PROTECTION

OF ENCLOSED

SPACES (ROOMS- CORRIDORS. ETC I CAN COVER LARGE

AREASNOT DETECTABLE

BY INTRUDER

EFFECTIVE AGAINST "STAY BEHINDS" NOT AFFECTED BY

AIR MOTION.

NOISE. LIGHT OR SOUND

COVERAGE DIFFICULT TO CONFINE TO DE

SIRED AREA

CAN BE SET OFF BY NEARBY FLUORES- CENT LIGHTS, LARGE

OBJECTS OUTSIDE PROTECTED AREA. RADIO TRANSMITTER

OPERATING NEAR

SENSOR FREQUENCY

HIGH IF PROPERLY

INSTALLEOCAN BE HIGH UNLESS PROPERLY PLACED AND CAREFULLY

ADJUSTED.

INFRARED MOTION SENSORS

AREA PROTECTION

ur ENCLOSED

SPACES (ROOMS. CORRIDORS. ETC 1 CAN COVER LARGE

AREASRELATIVELY IMMUNE TO

NOISE AND

VIBRATION

SOME SYSTEMS

SENSITIVE TO CHANGES IN THERMAL ENVIRON MENT (e 9 . CHANGES

IN SUNLIGHT AND

TEMPERATUREI

HIGH FOR RECEIVE ONLY SENSORS LOW FOR TRANSMIT

RECEIVE SENSORS

PHOTOELECTRIC

(ACTIVE) SENSORS

ACROSS DOORWAY

CORRIDORS. ETC . FOR PERIMETER

PROTECTION; MULTIPLE BEAM

SYSTEMS FOR

LIMITED AREA

PROTECTION.

HIGH DEGREE OF

FLEXIBILITY IN APPLICATION. INFRARED BEAM

DIFFICULT TO

DETECT. CAN COVER ACCESS

POINTS WHERE

PHYSICAL OB- STRUCTION NOT

DESIRED OR CAN NOT BE TOLERATEDNARROW BEAM OF PROTECTION

LINE OF SIGHT OPERATION- SMOKE OR DUST CAN HAMPER

OPERATION

SUBJECT TO MIS ALIGNMENT

PROBLEMS

LOW TO MODERATE.

WITH SYSTEMS

USING MODULATED

BEAMS HAVING

HIGHEST RESISTANCE,

CAN BE HIGH IF CERTAIN ENVIRON MENT FACTORS ARE

PRESENT (SMOKE. DUSTI OR POOR

PLANNING RESULTS

IN MISAPPLICATION.

PHOTOELECTRIC

(PASSIVE) SENSORS

POINT PROTECTION

USING SENSORS

WITH HIGH DIRECTION SEN

SITIVITY. LIMITED AREA PRO

TECTION OF SMALL ROOMS OR PORTIONS

OF LARGER ONES

RELATIVELY UN

AFFECTED BY ENVIRONMENTAL

FACTORS (EXCEPT ABRUPT CHANGE IN LIGHT LEVELI HIGH DEGREE OF

FLEXIBILITY IN APPLICATION

NARROW BEAM OF PROTECTION

LINE-OF SIGHT OPERATION. SMOKE OR DUST CAN HAMPER OPERA

TION.

CAN BE HIGH IF IMPROPERLY

INSTALLED SO THAT HEAT OR

LIGHT LEVELS ARE NOT CONSTANT. IF COVERS FLOOR. RODENTS MAY SET OFF ALARM.

CAPACITANCE SENSORS

PRIMARILY POINT PROTECTION FOR

SAFES. FILING CABINETS. VALUABLE OBJECTS. LIMITED AREA

AND PERIMETER

PROTECTION.

HIGH DEGREE OF

FLEXIBILITY IN APPLICATION. PROTECTIVE FIELD NOT DETECTABLE

BY INTRUDER.

CAN BE APPLIED ONLY

TO OBJECTS NOT

ELECTRICALLY GROUNDED. MAY

REOUIRE SPECIAL CONSTRUCTION.

VERY HIGH.

LOW IF PROPERLY

INSTALLEDVIBRATION SENSORS

PRIMARILY POINT PROTECTION FOR

VAULTS. SHOW

CASES. ETC.. LIMITED SPACE PROTECTION WHEN

INSTALLED TO PROTECT WALLS OR

CEILINGS. ETC

REOUIRE LOW MAIN

TENANCE.

HIGH DEGREE OF

RELIABILITY WHEN PROPERLY

APPLIED.

DETECTS ONLY FORCE

FUL ATTEMPTS AT

ENTRY CANNOT BE USED IN AREAS OF HIGH VIBRATION (TRAFFIC, CONSTRUCTION. ETC.I

CAN BE HIGH IF ENVIRONMENTAL

FACTORS ARE NOT TAKEN INTO AC COUNT MAY BE TRIGGERED BY MINOR EARTH

TREMORS. SONIC BOOMS OR TRAINS

17
The microwave field can be generated in all directions, just as light from a bare light bulb is radiated in all directions, or it can be transmitted

in a controlled pattern similar to the focused

light beam from a flashlight. Many manufacturers offer a variety of transmitting antennas to enable the user to select a field pattern that best suits his needs.

Bistatic microwave motion detectors utilize separate transmitting and receiving antennas

mounted at opposite ends of the space or area

to be protected. Monostatic units have the transmitting and receiving antennas mounted in the

same unit, sometimes using a single antenna to both transmit and receive the microwave signal.

The detection range of a microwave motion sensor is dependent upon the electrical power

of the transmitted field, the shape of the field, and the operating frequency. The most

commonly used frequencies are between 915

and 10,525 megahertz. ^

Microwave energy will penetrate and pass

through nearly all building construction material

(wood, sheetrock, cinder block, plastic, glass

and brick) and is reflected from metal. The

amount of penetration increases as the

microwave frequency decreases. Since the field from a microwave motion sensor will penetrate

walls, proper application is important. If the field

is not contained within the desired area or space, the microwave motion detector can

respond to motion in adjoining rooms, or to motion outside the building. On the other hand,

metal surfaces or structural steel within walls

and floors will reflect the microwave energy and

can distort the shape of the field so that the

detector will respond to motion in areas not expected to be included within the field.

The manufacturer's equipment specifications

will normally include sketches of the microwave

field shape for each antenna. The actual field of an individual unit will vary somewhat from that indicated in the manufacturer's literature. Each

antenna will, for the most part, have its own

unique transmission characteristics as a result

of normal manufacturing variation. Detection

ranges of several hundred feet are not uncommon for microwave motion detectors,

and these are frequently used in outdoor instal- lations.

Although various manufacturers incorporate

different processing circuitry into microwave

motion detectors, practically all systems

accomplish detection on the basis of frequency

shift. The basic logic of the alarm circuit can

use different criteria to interpret what signal will be judged to constitute an alarm. There will be

differences in the amount of frequency change

or the value of the integration time constant (the

minimum period of time that the frequency

change must be present) before an alarm is signaled. Some equipment is designed so that a

specific sequence of signal events must occur

before it will signal an alarm.

Ultrasonic Motion Detectors

Ultrasonic motion detectors operate on the

same principle as microwave motion detectors,

namely sensing the presence of an intruder

through the effect of his motion upon a field within a volume of space. In this instance,

however, the field is ultrasonic energy (high

frequency sound) rather than an electrical field. Most ultrasonic motion sensors generate

signals in the range between 19 and 40

kilohertz, which is above the frequencies that the average human can hear. Movement within

the field of ultrasonic energy generated by the

unit causes the frequency of the reflected signal

to change.

Ultrasonic motion detectors use a transmitting

element to generate the ultrasonic energy, a

receiving element to monitor the frequency of

the signal, and an electronic processing circuit that compares the transmitted and received

signals. As with microwave motion detectors, a

variety of signal processing techniques are used

by the various manufacturers.

Monostatic ultrasonic motion detectors enclose

the transmitting and receiving elements in a

single unit, and are used to protect a space of perhaps 6 by 9 meters (20 by 30 feet) in a room

with a ceiling up to about 3.5 meters (12 feet). These units are normally mounted on a wall or

at a ceiling corner. Bistatic ultrasonic motion

detectors employ separate transmitting and

receiving elements. Often, both elements are

located remotely from the processor, and the

system can be designed to use multiple

18
Microwave and ultrasonic motion detectors sense an intruder's motion ttirougti their energy fields. The

microwave motion detector transmits a high frequency electromagnetic field; the ultrasonic motion de- tector transmits a high frequency sound field.

receiving elements with a single transmitting

element. A typical installation would include a

single transmitting element mounted in the

ceiling near the center of the room, with two or more receiving elements, also mounted in the

ceiling, around the transmitting element. In some cases, bistatic units are designed to allow

the use of both multiple transmitting and

receiving elements.

Ultrasonic energy can be completely contained

within a room, for it will not penetrate most

structural materials, and it is, like any sound

energy, absorbed by carpet, draperies, and

acoustical tile. Obstructions within a room will reflect the ultrasonic energy, and will distort the

shape pattern of the transmitted energy. In addition, merchandise display cases, tables, or cabinets can block the ultrasonic signal, and

create blank spots. The detector will not respond to motion within such areas. Keep this

in mind if you use ultrasonic motion sensors in large warehouses, for if the size and location of stock piles of merchandise change often, the

detection zone of the sensor may also be

changed.

Infrared Motion Detectors

Infrared motion detectors are passive sensors, because they do not transmit a signal for an

intruder to disturb. Rather, a source of moving

infrared radiation is detected against the normal

radiation environment of the room. These

detectors are designed to sense the radiation

from a human body moving through the optical

field of view.

Infrared motion detectors are normally sensitive

enough to sense the moving radiation from a human at distances of 9 meters (30 feet) or more. Temperature changes of the room or

stationary items within the room do not cause

the infrared motion detector to sound an alarm.

Since these devices rely upon the differences in radiation between the room and an intruder, use

in a room that is maintained at a temperature

approaching that of a human body could limit the effectiveness of the device.

Infrared motion detectors use an optical system

to project an image of the area, within their field of view, onto a radiation sensor. Some of these

detectors employ a very narrow field of view

and are useful for point protection, to monitor a

long narrow corridor, or to provide line protection. Those designed to provide a wide field of view utilize either continuous area coverage or

multiple zone coverage. In the first type, the

detector will sense a moving source of radiation

anywhere within the image that is formed on the

radiation sensor. In the case of the zone type

detector, the radiation sensing element consists

19
Infrared motion detectors are passive; tliey do not transmit a signal. Instead they detect a source of moving

infrared radiation— the intruder—against the normal radiation environment of the room.

of many individual sensors, each located at a

specific point within the radiation image so as to sense moving radiation from a small area or volume within the total field of view. When using a zone type detector, alignment is critical. Wide

angle infrared motion detectors normally have a

field of view in excess of 90 degrees, and when

mounted in a ceiling corner can provide good

coverage of a 9 by 9 meter (30 by 30 foot) room. Infrared motion detectors with much

wider fields of view are available for use as wall- mounted installations.

Infrared Photoelectric Sensors

Infrared photoelectric sensors are another type

of optical sensor. A narrow beam of invisible infrared light is directed across a corridor, along a wall, or across a path that one would expect an intruder to travel. A receiver monitors the

beam, and signals an alarm if the beam is interrupted. The earliest photoelectric sensors used visible light, and are now often used to open the doors of grocery and department

stores.

Visible light, for obvious reasons, is not suitable

for use with photoelectric sensors for intrusion

alarm systems. Infrared photoelectric sensors

use infrared laser sources or white light sources and infrared filters. Many of the available sensors utilize high energy sources that are

capable of transmitting a beam over distances

of more than 100 meters (more than 300 feet)

and are most commonly used in outdoor

systems.

Frequently, the sensor's transmitter or light source and receiver are separate units; many,

however, mount the source and receiver in the

same housing. These systems, called retroreflection systems, require the use of a mirror to return the beam to the receiver. Mirrors can be

used with either type of infrared photoelectric sensor to direct the protective beam around the

entire perimeter of an area or along almost any

desired optical path.

Because the receiver is so designed that it will not signal an alarm as long as it is exposed to infrared radiation, it would be a simple matter to shine infrared radiation from a flashlight or other

light source into the receiver optics and thereby

defeat the system. Most infrared photoelectric sensors prevent such action by modulating the

light source. The light beam is transmitted as a

series of pulses rather than as continuous

radiation. The electronic circuit of the receiver is designed to signal an alarm if the received

radiation is not properly modulated.

20
A narrow beam of invisible infrared iigtit, monitored by a receiver, is directed across tfie expected

path of an intruder, if tfie beam is bro/<en, the monitor signais an alarm. Sound Sensors

Sound sensors detect intrusion by detecting the

noise created by the implennents used during an

attempt to breal< into a protected area or the

sounds produced by the intruder. These devices

consist of a microphone and an electronic processor. When the sound level increases

beyond the limit normally encountered in the

area, the unit signals an alarm. Sound sensors

are most often used to protect vaults.

Sound sensors respond to continuous noise,

such as that produced by drilling or sawing

through a structure, but can also employ

integration or pulse counting circuits. Pulse

counting is used to detect noise from

implements such as hammers, which do not produce a continuous sound. The integration

feature examines the noise detected by the

microphone over a short time interval, and an

alarm is signaled if the total energy

accumulated from all noise exceeds a preset

level. Thus, the noise from a single large pulse,

such as that from an explosion, will also cause

the sound sensor to signal an alarm.

In some instances, a sound sensor may be

used in an area that contains a source of audible noise, such as a compressor or a fan motor. Because such equipment only operates

intermittently, it is difficult to adjust the

threshold sound level to allow proper response

to intrusion noises. For such applications, sound

sensing units are available that permit the use

of a cancel-microphone in addition to the one

used to detect attack noises. The cancelmicrophone is placed close to the source of in- termittent sound, and the processing unit subtracts the cancel-microphone signal from

that of the intrusion sound sensing microphone.

Also available are sound sensor units that enable a guard to listen directly to the sounds

within the protected area by playing the

microphone signal through a conventional radio

speaker.

21
Vibration Sensors

Vibration sensors are used to detect the

presence of an intruder by monitoring the

vibrations produced when attack tools are used

to penetrate the structure members (such as

walls or floors) of a building.

The simplest of the vibration sensors is a mechanical switch designed so that the contacts

vibrate with the surface on which they are mounted. When the vibration level exceeds a

preset level, the contacts signal an alarm.

Contact microphone vibration sensors are used

for the same purpose. The microphone vibration sensor is an electromechanical device that produces an electrical signal proportional to its physical displacement. These devices operate on a principle similar to that of a phonograph

pickup and are used with a processor that is like the processor used in a sound sensor. In fact,

some sound sensing devices are designed to accept signals from both sound sensing

microphones and contact vibration

microphones.

Capacitance Sensors

Capacitance sensors monitor the capacitance

(capacity for the storage of electrical energy)

between specific metal objects and the

electrical ground of the earth. Any metal object

that is electrically insulated from the electrical ground of the earth will have a capacitance

associated with it. The capacitance sensor is connected to the metal object, such as a filing

cabinet or a safe. The electrical field sur- rounding the protected object is disturbed when

an intruder enters the field, causing the overall capacitance to change. The sensor signals an

alarm in response to the change in capacitance.

The electronic processing circuitry of the sensor can be adjusted to respond both to the total ca- pacitance change and the rate of change of the

capacitance of the protected object. These

devices can be used to protect one or more

objects, depending upon the design of the

sensing circuit.

Capacitance sensors can be used with grid

wires or screens to protect an area such as a

wall or a window; however, such use is not

frequently encountered.

A capacitance sensor detects a change in the electrical field surrounding an object when an intruder

enters that field. This change causes the alarm to go off.

SYSTEM DESIGN CONSIDERATIONS

The nature and location of your business will have an important bearing on the design of an

appropriate alarm system, for these factors will

in general dictate the perimeter and interior protection that is needed. The design of a system

that achieves the desired degree of protection

depends largely on the layout of your facilities and your routine operating procedures.

The floor plan of your business is the basic consideration in the selection and location of the

required sensors. Your business practices are

the basic consideration in the design of the

operating modes of the alarm system, which in turn will dictate the selection of the control unit.

All of the above factors must be considered in order to determine the need for tamper protection. The basic system design will, of course,

also depend on the manner in which the alarm

signal is to be transmitted—a topic of separate

discussion.

22
The Floor Plan

When you analyze the threat to your business

and consider the alternative types of protection,

you will find that a floor plan of your premises is a valuable aid. The floor plan should note all doors and windows, room sizes, skylights,

interior doors to basements, and the location of high value items.

You can quickly trace the likely routes of an

intruder and identify the locations that you might

wish to protect with point or volume sensors. You should also consider the types of equipment or sources of false alarm stimuli at various locations within the premises. Similarly,

you should also study the various locations to determine which areas are routinely available to the general public or customers during normal

\^.Jrr%i • ULTRASONIC MOTION DETECTORS

INFRARED PHOTOELECTRIC SENSORS

H PRESSURE MATS

A floor plan of your business will help

tection. This type of protection ' also tells you which zone he is in.

lan or your ousiness win neip you determine if it is necessary to divide your store into zones of protection. This type of protection not only lets you know an intruder is on the premises of your business, it

23
working hours. This last factor will help you to determine the need to protect the sensors or other alarm components from being tampered

with by an individual planning a return to your

business after normal working hours.

The floor plan is also very useful when you

compare proposals from each of the several

alarm installers that you have asked to provide

quotations. Marking a copy of the floor plan to show each sensor and its location as proposed

by each bidder can help you quickly isolate the

basic differences among the proposed systems.

When the basic differences have been

determined, you should ask each bidder to explain his choice in detail. It could be that he

has recognized a need that you or the other

installers have failed to consider, or he might be

basing his selection upon experience and/or a

specific product line that he routinely sells.

In most cases, the tradeoffs proposed by each

alarm installer will be obvious. One installer might choose to protect display windows with

only metallic foil, while another might prefer to use a pressure mat along the floor below the

window, or perhaps use an ultrasonic motion sensor to protect the entire portion of the

building behind the window and the door. When

you review the proposal, you should include on

the floor plan the protection volume or envelope

of the sensor.

The floor plan will serve an additional purposeit will help you to determine whether it is appropriate to separate the system into zones

of protection. For example, if your facility

includes a warehouse that is infrequently visited during the normal working day, you might

choose to keep that part of the alarm system

active during normal working hours although the

rest of the system is turned off. Similarly, if you

include a system to protect against shoplifting,

this would be a separate circuit, or zone. In the case of a larger business that covers a large

floor area, such as a major department store, it is desirable to incorporate multiple zones so

that the police or guards who respond to an

alarm can go directly to the area where the

intruder has been detected.

If you operate a small business located in a

typical suburban neighborhood shopping center.

characterized by the glass front and dropped

acoustical tile ceiling, take a good look at the

space above the ceiling tile. You will probably

find that there is no barrier between your space

and that of the adjoining businesses. If this is the case, you are vulnerable to an intruder who

enters a business at one end of the row, climbs

into the overhead space, and travels to any

store in the complex. Perimeter protection alone

is inadequate under such conditions.

Control Units

Individual intrusion alarm sensors are usually

connected to a master control unit that receives

their signals and causes a local alarm to sound

or alerts the police or the central station to the

fact that your system has entered the alarm

state.

Unless you have selected a system that does

j the job by low-power radio, it will be necessary ! to connect the sensors to the control unit with , electrical wire. In that case, you will have to ' choose between visible wiring that is strung

along the walls next to molding or completely i concealed wiring, which is considerably more | expensive to install.

The type of control unit that you select will depend upon the sophistication of your overall

intrusion alarm system. In some cases, the

control unit can be a part of one of the

components. For example, if you determined

that a single ultrasonic motion detector with a j local alarm would adequately protect your busi- j ness, without the need to install perimeter pro- j tection, the ultrasonic unit would provide relay \ contacts that would turn the local alarm on and ( off. J

More complex alarm systems, however, will have a separate master control unit. This unit

j; will provide separate input circuits for each ) alarm zone that you wish to incorporate into i| your system, and it will also provide the n electrical current that flows through the switch j sensors. It may also be used to provide the ; electrical power for the other sensors.

24
Individual intrusion alarm sensors are usually con- nected to a master control unit that receives their

signals and sets off a local or remote alarm.

The control unit is the source of bacl<up or standby power for at least the switch sensors. Should your neighborhood have a complete

electrical power failure, the intrusion alarm

would be inoperative without standby power.

Standby power requirements, to insure protection during a power failure, are the subject of debate and depend upon the nature of the busi- ness. Installers recommend a 4 to 12-hour

capability of operating from standby power.

However, financial institutions are required to have a 72-hour capability of operating from

standby power.

Batteries are used universally for standby

power. Some equipment uses conventional dry

cells, which must be replaced when their shelflife is at an end. Other equipment uses

rechargeable batteries. In some equipment, the

batteries are wired to a low-power charging unit, called a trickle charger, which maintains the

batteries in a fully charged condition as long as

the system is connected to electrical power. If the equipment does not include a charger, the

batteries must be periodically checked and fully

recharged when necessary.

If the control unit or a sensor contains an

integral battery charging circuit, you should

determine the power capacity of the charging

circuit. If the charger cannot operate the sensor and simultaneously recharge the battery, you

could have a problem. Some of the equipment

that has been tested did not have sufficient power capacity. In those cases, when the line power was restored after a power failure, all of

the power went into charging the battery and

the detector provided either greatly reduced or no protection until the battery had been

recharged.

The control unit will normally incorporate a keyoperated selection switch that you use to place

it into the appropriate mode of operation. This

may have only two positions (on and off) or it may also include a test position. The test position places all of the sensors in operation

and allows you to test each component of the

system without sounding a local alarm or transmitting a signal to the police or central station. Since your system will require periodic mainte- nance and checking, make certain that you

have this test capability. Control boxes that are used for both intrusion detection and holdup protection will have still another selection position.

In this case it will probably be labeled off, day,

night, and test. The day position places all components associated with the holdup alarms

or shoplifting devices into operation while

turning off the sensors on doors. Obviously, the same position can be used to operate specific zones (such as an alarm zone for an unmanned

storeroom) and not only holdup sensors. The

control unit should provide visible displays such

as lights or meters that clearly indicate the

operating status of the intrusion alarm system.

For obvious reasons, the control unit within your

premises should be in a location that is accessible only to you and your authorized

employees.

In addition to the master control unit, used to set the intrusion alarm system to its desired

operating mode, you may wish to use a remote

off-on switch. This is normally installed on the

exterior of the building near the door you

routinely enter and leave when the building is unattended. It enables you to turn the system

25
off when you enter in the morning, and to activate it from the outside at night.

Alarm systems connected to central stations do

not normally use a remote control switch.

Rather, the system is turned on and off by the

central station; the individual operating the

system notifies the central station when he

leaves, and any alarm is disregarded. In the

morning, a signal is transmitted to the central

station when the alarm is switched to the day

position, and the central station knows that the

entry was by an authorized person, even though

the system sent out an alarm when the door was unlocked and opened.

Some alarm systems incorporate a feature

referred to as an exit delay. With this feature,

the alarm system does not enter the secure mode (armed and ready to respond) for a period

of time such as 15, 30, or 45 seconds after it has been activated. This allows the operator

sufficient time to leave the premises without

causing an alarm to sound when he opens the

door to leave. Such systems may also

incorporate an entrance delay, which will permit

the alarm to be shut off before a signal is trans- mitted when entering the premises.

Correct opening and closing procedures are

essential when a remote alarm system is connected to either a police department or a

central station.

Tamper Protection

A sophisticated intruder often has a working

knowledge of alarm systems and components.

Such an intruder is capable of disabling an

alarm system if he has access to circuitry or adjustment controls. For example, a switch sensor that is used in a normally closed circuit, the most popular method of wiring, can be

defeated by simply connecting a jumper wire across the contact terminals.

Tamper protection is a desirable feature for intrusion alarm systems used in commercial

applications. The simplest method of providing

some degree of protection is by the use of tamper switches. The tamper switch is usually a

mechanically actuated switch that is mounted

within the equipment enclosure or cabinet. The

switch signals an alarm if the cover is opened.

In addition to their use on cabinets, tamper

switches are also used in sensor enclosures

and in control units.

Exposed wiring between components is also vul- nerable to tampering, and for that reason many

alarm systems incorporate line supervision, particularly between the control unit and the central

station or police department receiving

equipment. This is accomplished by means of a

separate alarm circuit that monitors the

impedance of the lines. An end-of-line resistor

is often used for this purpose and is wired in parallel across the terminal at the point where

the wire is connected to the control unit, or to a component. This resistor provides a fixed

reference impedance that will change if the

wires are cut, or if jumper wires are connected

to the lines. An alarm will be transmitted if the

impedance changes by more than a specified

amount.

Line supervision also makes it possible to detect problems, such as a line that has been

damaged by a severe rainstorm, by means of the transmission lines themselves.

Other types of line supervision are also used

and include the transmission of coded signals

between components for very high security

systems. This type of supervision enables one

to check the status of the various components

and locate line problems, or to detect attempts

to introduce external signals into the transmission line in an effort to defeat the system.

A tamper protection device sets off an alarm when

an intruder tries to defeat a protected component

of tfie alarm system—in this case, the control unit.

26
INSTALLATION AND OPERATIONAL CONSIDERATIONS

The proper installation and operation of an

intrusion alarm system are the , keys to its effectiveness. Even good components,

appropriate for the application but improperly

installed and operated, will perform poorly. The

result of improper installation can be a system

that quickly becomes an annoyance by

constantly generating false alarms or one that provides little protection. As with any electromechanical system, proper maintenance is required on a routine basis.

Environmental Factors

Building vibrations induced by wind, vehicles

moving outside the building, or heavy machinery

are troublesome to most sensors. In fact,

excessive vibration will cause a motion detector

to signal a false alarm, in most sensors there can be a gradual loosening of adjustment or alignment screws that will impair the operation

of the unit. Vibration of a photoelectric unit could change the aim of the beam and result In less than optimum operation. As previously

mentioned, there are several sensors that are designed to signal an alarm in response to

vibration and the effect of extraneous vibration

upon such devices is obvious.

Temperature and humidity must also be taken

into account. Sensors installed in an uncontrolled temperature area (such as a garage, a warehouse, or a barn) may be subjected to extreme temperatures that are not within their operating range. It is difficult to predict the

effect that temperature or humidity will have

upon a particular sensor. One unit may cease to

function, while another may decrease in detection sensitivity so that the unit is no longer

reliable and yet a third could increase in sensitivity so that an alarm would sound constantly.

Excessively high or low humidity can alter the

detection characteristics of ultrasonic motion

detectors and capacitance sensors. If you

intend to install alarm system components in areas with extreme temperature and humidity

variations, the equipment specifications should

be carefully examined. If the manufacturer

cannot assure you that the equipment will

operate satisfactorily in your environment, look

for another supplier.

Electromagnetic interference is another problem

that is common to all equipment. Radiated

interference can be due to transmission sources such as patrol car radios, or it can come from

natural disturbances such as electrical storms. With few exceptions, the equipment that has

been tested by the Law Enforcement Standards

Laboratory was susceptible to electrical fields of the type produced by police radios, other

emergency communication equipment, taxicab

communications, and radio or television

stations. The problem Is minimized when the

equipment is mounted In a building that provides electrical shielding because of metal

construction or reinforcing steel. If your busi- ness is located near a TV station, you should be aware of the potential problem and discuss it in detail with the installer. You should also keep

this problem in mind If you employ Internal guards who use portable transceivers. Perhaps

you will find it necessary to identify specific areas within your premises where transmission

is prohibited.

The second type of electromagnetic

interference is conducted, or power line, interference. When a compressor motor starts, or other equipment Is turned off and on, it can

induce a voltage surge In the power lines within

your building and cause the system to generate an alarm. Fortunately, most alarm components

are not overly susceptible to this type of Interference. However, it is a good idea to connect alarm components to a separate

electrical circuit. There is a simple test that you can make if you suspect that an alarm

component is susceptible to conducted

Interference. Plug a normal desk top fluorescent

reading lamp (one with a separate ballast unit) into the same line as the component and turn the light on and off rapidly. If the component

enters the alarm state, the chances are that It is not very resistant to power line interference as

a source of false alarms.

27
A momentary drop or increase in the line voltage is also a potential problem for an alarm

system. Most of the equipment tested by the

Law Enforcement Standards Laboratory

operated satisfactorily over a range in line voltage from 85 to 110 percent of the rated

voltage. If you anticipate a wider range of voltage, it is suggested that you check with the

supplier before you purchase the equipment.

Sensor Installation Factors

Selecting components that are suitable for the

intended use, compatible with the operating

environment, and installing them in accordance

with the manufacturer's instructions will afford

you an intrusion alarm system that will provide

trouble-free, effective protection.

Before you install any sensor in an area that you believe to represent a marginal application

for the device, try to use a test unit at the

location on a temporary basis. Let it operate for a few days and see if it performs the way it should before you install one as a permanent

part of your system.

Perimeter or Linear Protection. The most

popular switch sensor is the magnetic switch.

When considering a magnetic switch for use on

a steel door and frame, make certain that it is designed for such use. In some cases, it might

be necessary to mount the switch on special

spacer blocks that place the switch and magnet

a sufficient distance from the steel surface to allow proper operation. After a balanced

magnetic switch has been mounted in its permanent location, it will be necessary to adjust the balancing magnet. In some instances

you might wish to have versatility, so that a window can be partially open for ventilation and

yet be protected by the switch sensor. This can be accomplished by mounting a magnetic

switch in a suitable location with the window

open and a magnet positioned directly opposite

the switch. A second magnet is then mounted

so that it operates the switch with the window

closed.

The movement or displacement required to actuate a magnetic switch is important. If the

switch is actuated by a very small displacement,

it may cause false alarms when the wind or

normal building vibration causes loosely fitting

doors or windows to rattle. This is also a common problem with mechanical switches.

Obviously, the switch should sound an alarm

before the displacement is so great that one

can enter or reach in and tamper with the

switch.

Normally, mercury switches are used only for a window or trap door, such as a transom, that

opens by pivoting around a horizontal axis. It will be necessary to adjust the switch after mounting so that it actuates when the door or window has been tilted to the maximum

permissible position. Since a mercury switch is mounted on the moving member, rather than

the window frame or door jamb, the connecting

wire is subjected to the stress of bending each

time the window or door is opened or closed. In such instances, the installer will normally use a door cord, which is a special wire designed to withstand repeated bending. Door cords are

also used to make connections to metallic foil on swinging glass doors.

Photoelectric sensors require careful alignment

of the optical system, particularly if the system

uses mirrors to route the beam. The transmitting

and receiving units as well as the mirrors must

be rigidly mounted and the adjustment should

incorporate a clamping mechanism to retain alignment once the system has been set up. While some of these units are contained in housings that are mounted flush with the

surface of the wall, others are mounted on the

surface of the wall. Such units are subject to unintentional shocks, as from cleaning personnel

using brooms, etc., that could disturb their alignment. Most of the tested photoelectric units

have performed well; however, proper alignment was difficult to achieve with some of the units.

Point, Spot, or Object Protection. Sound

sensors and microphone vibration sensors designed to respond to attempts to penetrate or break through walls are most often used to protect vaults and similar massive structures. These devices have been found to perform

reasonably well when installed and operated in accordance with the manufacturer's

instructions. The use of these devices in other

applications should be carefully considered,

because normal structural vibrations and noise

28
from aircraft, trains, trucks, etc. may induce

sound levels and vibrations of sufficient intensity to cause false alarms.

Contact vibration sensors are used primarily for vault protection. These devices are inexpensive

and can be quite useful; however, care must be

exercised when installing them. Some manufacturers recommend installation with pressure

sensitive tape, which can change the vibration

response characteristics of the device; the

overall response might also change as the tape

ages. It is better to use several of these devices

to protect a length of wall than to use a single

unit set to a very high sensitivity. Their

placement with respect to structural members

as well as the construction of the wall are

important. These devices are not precision

devices and rely upon spring tension for the

adjustment of vibration sensitivity. Tests have

proven that contact vibration sensors are quite

difficult to adjust for proper operating sensitivity.

Capacitance sensors use the metal object being

protected as one plate of a capacitor. These

objects, such as filing cabinets or safes, must

be electrically insulated from earth ground or the ground of the building. Units are available

with both fixed and variable capacity and in a

range of sensitivities that will allow as many as

a dozen file cabinets to be protected by a single

unit. It is important to make good electrical contact with the item that is to be protected.

Many of these units incorporate an automatic

compensation circuit to accommodate changes

in the room environment, such as temperature

and humidity, which can affect the sensitivity of the detector. Be sure to obtain this feature if the

equipment is to be used in a room that is not temperature controlled. The majority of the ca- pacitance sensing equipment that was tested

performed well in all respects.

Area, Space, or Volume Protection. Microwave

motion detectors transmit energy that will penetrate many materials. To avoid false alarms, you will want to contain the detection

field within a single room or area. Thus, if the

building has large display windows, or drywall

partitions, you must select the antenna pattern

carefully. Metal surfaces or objects will reflect the energy, causing large distortions of the

normal pattern, and it is not uncommon to find

that motion is detected in areas that are not expected to be included in the antenna pattern.

If the energy escapes to the exterior of the

building, pedestrians, moving vehicles, and

swinging signs can all become sources of false alarms.

Because it is possible to use an antenna

capable of producing a narrow beam that extends more than a hundred meters (several

hundred feet), the microwave detector can be

used to detect motion anywhere within a long

corridor in a building. Similarly, some installa- tions have taken advantage of the fact that the

energy will penetrate building partitions and so have used a single detector to protect two or more rooms. A satisfactory installation of this type can be difficult to accomplish, particularly If the rooms have metal desks or furniture, or other potential reflection surfaces.

Tests of microwave motion detectors have

shown that some are quite sensitive to

vibration, and many will generate false alarms in response to a flickering fluorescent light. Draperies that are set into motion by heating or

air conditioning air currents are also a source of false alarms.

Ultrasonic motion detectors are more frequently

used than microwave motion detectors. Since ul- trasonic energy is transmitted directly by the air within a room, air currents themselves can be a

source of false alarms and a unit should not be

installed close to a ventilation duct. Moving

draperies can also cause false alarms and

some units operate on a frequency that Is present in the ring of a telephone bell, another source of false alarms. Similarly, a false alarm can be caused by a squeaky hinge, by air being

sucked beneath a closed door by a vacuum

cleaner, or by escaping steam. While ultrasonic

energy is generally well contained within a

room, it is possible that small amounts of the

transmitted signal can pass through cracks,

under doors, etc. If separate ultrasonic motion

detectors are used in adjoining rooms, make

sure that both units operate on the same

frequency, and synchronize the transmission of

the two signals.

Infrared motion detectors must also be mounted

on surfaces that are not subject to building

vibration. Tested units have performed well.

29
although alignment was sometimes difficult. Most of these detectors are not sensitive to sunlight passing through window glass;

however, some will respond to small beams of

direct sunlight reflected from moving Venetian

blinds or from the floor. Try to locate such

detectors so that they are not exposed to reflected energy sources.

After the Installation

Once the individual sensors have been installed and connected to the control unit, it will be

necessary to adjust them for proper operation

and then test each sensor to be sure that it is working as intended. Your control unit should

have a test position that will allow each

component to be tested without sounding the

alarm.

Pay particular attention to the motion detectors

and their adjustment. Any electronic device will demonstrate less than best performance if it is pushed to its electronic and sensitivity limits. Some installers have made the mistake of

attempting to use a single ultrasonic sensor to provide protection for an area that is slightly

larger than it was designed for. This can be

done by adjusting the sensitivity to its maximum

setting, but will result in a system that false- alarms routinely. The only solution is to reduce

the sensitivity, which means that portions of the room will no longer be protected. Similarly, if an

ultrasonic or microwave motion detector is installed in an environment that contains false alarm stimuli, often the first action taken is to reduce the sensitivity in hopes of eliminating the

problem. It is not uncommon to find that the sensitivity has been reduced more than once, and

the unit is finally set at a sensitivity so low that the detector will not sense the presence of an

intruder. When you use motion detectors, it is desirable

to use those that incorporate a visible walk-test

indicator. This can be a light which, when the

unit is switched to the test mode, comes on whenever the detector enters the alarm state. A

meter can be used instead of a light. You can

then walk throughout the room and observe

whether your motion has been detected. When

you perform this test, walk only two or three

ONCE INSTALLED ~1

V ADJUST

V TEST(on normal & standby power)

V INSPECT

V MAINTAIN

ALL PARTS OF SYSTEM

steps and stop. Once the detector has alarmed,

you will have to wait a few seconds until it resets and the indicator goes off before you try another test.

If any of the components of your alarm system

include tamper protection circuits, be sure that

the installer demonstrates that these circuits are

operational. While not a common occurrence,

there have been occasions when installers have

neglected to connect the tamper protection

circuits of alarm systems and it was not discovered until the systems had been

compromised by an intruder. Similarly, make

sure that the system operates properly on

standby power, if this capability is provided.

When the installation has been completed to your satisfaction and you assume the responsibility for its daily use, be sure you establish and

follow a routine maintenance schedule in accordance with the manufacturer's recommendations. The batteries of wireless systems will have to be checked periodically and replaced on a fixed schedule, usually about once a year.

*

Similarly, standby power supplies must be • checked and nonrechargeable batteries

replaced on a fixed schedule. Rechargeable

batteries normally have a life-time of many

;

years.

Some components may require periodic ! cleaning to remove dust or other accumulated f foreign matter, and many will require minor

'

electronic adjustment from time to time. ^

All of the sensors should be tested on a routine ^ basis to be sure that they remain operating, for J equipment failure is always a possibility. For i example, laboratory tests have established that

it is not uncommon for mechanical switches,!

and to a lesser extent magnetic switches, to fail i;

30
after a limited number of opening and closing

cycles. While a minimum of 100,000 cycles of operation without failure is considered to be

mandatory for alarm system use, a switch can

fail after as few as fifty cycles of operation.

The other system components should also be

checked periodically. Examine door cords to be

sure that the terminal block connections are still tight, and that the cords are not showing signs

of wear. If you use window foil, be sure that normal cleaning operations have not damaged

the protective coatings or the adhesive that bonds it to the glass. Be sure to check sensors mounted on brackets or othen/vise attached to the building to see if bolts or screws need to be

tightened. If you use money clips in cash

drawers, carefully examine the lead wire for evidence of wear. This wire is subject to constant stress as the drawer is opened and

closed, and it is not uncommon for the wire to break from fatigue.

The periodic inspection of the entire system will also ensure detection of any evidence of attempts to tamper with it, alerting you to the

fact that someone may be planning to break

into your facility.

Unless you have a large and complex intrusion

alarm system, routine maintenance and

inspection is neither difficult nor time

consuming. Frequently, the maintenance and

Inspection of the intrusion alarm system will be

a part of an overall service contract, relieving

you from this responsibility.

SOUNDING THE ALARM

The type of alarm signaling/transmission

system you should use in your particular

application depends upon the location of your

place of business, the frequency of police

patrols, and your ability to afford the cost. Remember that, after deterrence, the purpose

of an alarm is to summon the proper authorities

to stop a crime during the act of commission or

lead to the apprehension of the intruder. To this end, it is important that the response to the

alarm comes in the shortest possible time.

Four types of alarm signaling systems are in general use: the local alarm, the central station

system, the automatic telephone dialer system,

and the direct connect system. It Is advisable

for you to check the local ordinances and codes

concerning electronic intrusion alarm systems.

There may be regulations governing the types

of alarm systems that you can install, to whom

the alarm may be transmitted, or the length of time a local alarm can be sounded.

Local Alarm System

Local alarm systems provide on-the-premises

Indications, usually by means of bells or lights, that an attempted or successful intrusion has

taken place. You are, therefore, relying on someone hearing or seeing this signal and

calling the responsible authorities. In today's

densely populated urban regions the local alarm

may often go unnoticed or fail to elicit any

responsible reaction. In less populated areas, there may be fewer chances that someone in your neighborhood will be present to hear the

alarm; therefore, the appropriateness of a local alarm is sometimes questionable.

The local alarm also serves to notify the burglar

that he has been detected. This may be advantageous in frightening off the less experienced

intruder before he can finish his intended act. On the other hand, during a holdup for example, a local alarm indication may provoke the robber

and cause him to harm people in the area. A local alarm system is less expensive than

other types. It does not require the leasing of telephone lines for the transmission of signals;

the equipment itself is often relatively simple, unsophisticated, and less expensive to install and

maintain. Because of their simplicity, however,

local alarm systems can be defeated by a

burglar with relatively little trouble. Law enforcement officials generally prefer one of the silent forms of alarm transmission. In some areas, so

remotely located that neither police nor private

security agencies could reach the scene in time

to apprehend an intruder, the local alarm is probably the only practical type of alarm to use,

in hopes of frightening the Intruder away or

alerting a chance passerby.

31
Some intrusion alarm systems use a local alarm

in combination with a remote (silent) alarm. In these installations, the silent alarm is transmitted immediately when a sensor is actuated. The

local alarm is generally sounded on a delayed

basis, usually several minutes after the silent alarm has been transmitted. This alarm

sequence is intended to give the police time to respond to the alarm, while minimizing the time

that the intruder has to perform his criminal act. There are also intrusion alarm systems that sound a local alarm simultaneously with the

transmission of a silent alarm.

Central Station System

If you choose a commercial central station

system to supply your intrusion alarm needs, a

signal indicating an attempted intrusion on your

premises will be sent directly to a remote,

continuously staffed supervisory station, usually

by way of a leased telephone line. The demand

for leased, or dedicated, telephone lines is so

high in many localities that alarm companies

have a difficult time obtaining them. As a result,

some central station systems will use a "McCulioch loop" for transmission. This

equipment allows 12 or more alarm subscribers

to share a single leased line. Such systems are

only slightly less secure than a direct wire

connection, and may result in a decrease in the

monthly leasing costs. Since leased wires are expected to become increasingly difficult to obtain, future installations will be forced to make increasing use of shared lines, and the

alarm companies may also find it necessary to use radio transmission of the alarm signals.

Since a central station alarm system is a commercial service, the degree of protection

you use will determine the price you pay. The

types of services offered range from the

monitoring of alarm signals and notification of the law enforcement authorities to dispatching

private guards to your premises when an alarm

has been transmitted. Central station systems

usually maintain and repair the equipment they

provide. Commercial services of this type

usually employ well-trained personnel. Typically,

however, you have less authority over the

operation of the system and may not know the

system is in need of repair. Similiarly, unless the

central station informs you, you may not be aware that there has been a telephone line failure during a certain period of time. Often

central station personnel are given keys to the

protected premises so that they may enter in case of an alarm. While central station services are probably the most highly supervised, you

will find that they are also the most expensive.

Automatic Telephone Dialer

Two types of automatic telephone dialers are

available, the tape dialer and the digital dialer. Dialers offer the advantage of using less costly

public telephone lines instead of leased lines and may be adequate for low security

applications. A tape dialer can deliver a prere- corded or coded message to a central station

office, to a private answering service, to a

neighbor, to yourself, or (if local ordinances

permit) directly to the police. Many of the earlier tape dialers were a source of constant

problems to police departments. Since these

devices were quite unsophisticated, they would

dial the number of the police department and automatically start to play the prerecorded

message after a specific time delay, generally a

period of time equal to the time required for the

telephone to ring three or four times. It was not uncommon for the dialer to play most of the

message before the police were able to answer

the phone. As a result, the police knew that an

alarm had been sent, but did not know its location. In addition, these systems often seized

the police telephone line, and would keep the

line open until physically shut off at the dialer

unit itself. Thus, the police department tele- phone lines were tied up for extended periods.

In addition, it was common for the tape

transport mechanism to malfunction and deliver no message at all.

Most modern tape dialers have solved the

problems of the earlier units, and are reasonably reliable. Many include circuits that delay the message transmission until the tele- phone being called is actually answered. In fact,

most dialers are capable of dialing two or more

numbers in the event that the first one dialed is busy or does not answer. Many of the dialers

also permit the transmission of fire alarm

messages through a separate channel. Some

32
ALARM SIGNALING/TRANSMISSION SYSTEMS

LOCAL

_^^^TRUs!^^^ SETS OFF ^

ALARM SYSTE

ON-PREMISES

ALARM SIGNAL

• BELLS

• LIGHTS

• SIRENS

M

^.'-''POSSIBLE^^

1 RESPONSE BY

]

• NEIGHBOR

• PASSERBY

L • POLICE J ^vPATROL

CENTRAL STATIOW SYSTEM

AUTOMATIC TELEPHONE DIALER SYSTEM

DIRECT CONNECT SYSTEM

Hi 33
tape dialers also include circuitry that prevents

the dialer from being defeated by incoming calls on the dialer's line.

The digital dialer does not use a recorded tape

message. It is a solid state, electronic device

that transmits the alarm message as a series of coded electronic pulses. This alarm signal can

only be received by an electronic terminal that can process and decode the message,

translating it into a form that can be interpreted

by the individual monitoring the receiving

equipment. In some instances the alarm is typed out by Teletype equipment, while in others it is directed to a conventional alarm

display. The digital dialer equipment offers

distinct advantages, for it is possible to include

circuitry that allows the receiving station to provide line supervision, and to check the status

of the dialer on a routine basis.

In some cases, the receiving terminals for digital

dialers are connected to small computers that provide additional data such as the type of establishment, location of alarm sensors, etc., to be displayed for the operator.

Because a special receiving terminal is required,

digital dialers are used almost exclusively in central station alarm systems. A few police

departments, however, have installed receiving

terminals that will accept alarms from digital dialers.

Since both tape and digital dialers use normal

telephone transmission lines, their use is subject to approval by the telephone company.

In some cases, the telephone company may

require that a coupling circuit be leased directly

from them, while in others, it may be acceptable

to install a coupling circuit (modem) that meets

with the telephone company's approval, but is not purchased or leased directly from them.

Direct Connect System

In a direct connect system, your intrusion alarm

system is directly connected by wire to a remote alarm receiver located either at police

headquarters or at some other location. Unless

your establishment is a financial institution, local ordinances may not permit direct reporting to police stations. A variation of this concept is the

TABLE 3. THE RELATIVE EFFECTIVENESS OF PROTECTION SYSTEMS

ROBBERY BURGLARY THEFT

PHYSICAL PROTECTION*

(NO ALARM SYSTEM) o o o

COOPERATIVE SYSTEM (g)^ • •

LOCAL ALARM

AUTOMATIC DIALER <g) (g)

DIRECT CONNECTION TO POLICE • •

CENTRAL STATION • •

PROPRIETARY SYSTEM W/

IN-HOUSE SECURITY FORCE • •

• EXCELLENT

(g) GOOD

O FAIR

*The effectiveness ratings assume that the protected premises have adequate physical security. If not, each

rating should be reduced one level, e.g., from excellent to good.

Assumes that someone other than the victim can actuate the alarm.

34
cooperative or "buddy" alarm system. In this system the alarm signal, either by direct wire or through the use of an automatic telephone

dialer over the normal telephone lines, goes to a nearby business establishment or residence

where a designated individual receives the

signal and phones the appropriate law enforcement agency. In this case you should be certain

that the one who receives the alarm signal

knows the proper procedures for notifying the

police.

The charges for leasing telephone lines for alarm system applications, which are usually

regulated by public service or utility commissions, involve a small fraction of the

total cost of your system; in many localities there are several grades of lines available, at varying costs. The cheapest alarm lines are not as good as the voice grade lines. While the

actual charge for leasing a telephone line varies

from area to area, there is usually a

nonrecurring installation charge and a monthly

service charge. If you decide to use a central

system service, the telephone line charges are

billed to the central station and added to your

contract.

GETTING YOUR MONEY'S WORTH

As discussed earlier, the economics of installing an intrusion alarm system involves a business

decision that only you can make. The factors

that enter into this decision are numerous, and

the bottom line of the analysis is the cost to

install and operate the system that meets your

needs. It goes without saying that, as a businessman, you want to get your money's worth.

The first step in achieving this goal is to be

certain that you have properly evaluated your

security needs. The flow chart on page 36

serves to outline the steps that enter into the

selection of an optimum intrusion alarm sys- tem. Use this chart as a means of insuring that

you have not overlooked any factors that should

be considered. Table 3, the comparison of the

relative effectiveness of the various types of

protection, and Table 2, the brief summary of

the advantages and disadvantages of the var- ious sensors with respect to their use in dif- ferent applications, will also be convenient

references.

The cost of installing and operating an alarm

system will vary significantly depending upon

the type of system and the community in which

your business is located. As a rule of thumb,

you can expect that the cost of installation will be approximately equal to the cost of the

components that make up your system. Each

alarm installer will have his own method of estimating the price of the system. However,

whether or not each item is separately costed.

the bid should clearly identify the components

that will be used and where they will be located on the premises. Thus, regardless of the bid

method, you will be able to compare the

systems that are proposed. Obtain quotations

from several alarm installers, and get all quotations in writing.

Investigate the firms that you ask to provide

quotations. In addition to checking with the

Better Business Bureau, ask for references, and

ask your local police if they have had particularly good or bad experiences with any firm that

you consider hiring to provide your system.

Make certain that the firm has the proper

license if your community requires one. In addition, check to determine whether the local

installers are members of trade associations.

There are several national and regional

societies or associations open for membership

to alarm companies and installers. These

associations attempt to keep their members

current with alarm system technology, and

within limits (as with any voluntary membership

organization) they attempt to insure that their members uphold high standards of business

practice.

There are two methods for procuring an alarm

system: buying and leasing. There are responsibilities as well as advantages in direct ownership of the equipment. For example,

although you make a larger initial cash

investment in purchasing the system, you will be

35
able to depreciate the cost of the hardware.

You must also realize that the sophisticated

electronics involved in many systems will require periodic maintenance (this is applicable

whether the system is purchased or leased). In leasing a system, maintenance is usually

provided as needed and periodic inspections are made. Therefore, you should consider all the costs (that is, purchase price versus initial leasing costs, service contract costs versus

periodic maintenance, etc.) over the number of years you feel the system will be in operation.

You are considering the use of an electronic

intrusion alarm system because of the value of your property and merchandise as well as the

value of human life that may be involved should a robbery take place on your premises. Thus,

beware of "bargain" systems. Such systems

may prove unworkable or easily defeated by an

intruder. Prior to signing a contract for any

service you should also make certain that the

alarm system company with whom you are

dealing will provide maintenance or service on a

continuing basis.

TO EVALUATE YOUR SECURITY NEEDS

DETERMINE

SELECT

TYPE OF THREAT

• BURGLARY

• LARCENY/THEFT

• VANDALISM

• ROBBERY HOLDUP

• ARSON SELECT

TYPE OF PROTECTION

• POINT • NO ALARM

PERIMETER SYSTEM

•• AREA

• HOLDUP

TYPE OF ALARM

LOCAL REMOTE

• AUDIBLE • AUTOMATIC

TELEPHONE

• VISIBLE DIALER

• LEASED LINE • DIRECT CONNECT

TYPE OF SENSOR

• ELECTROMECHANICAL • MOTION

® PHOTOELECTRIC • SOUND

9 VIBRATION • CAPACITANCE

® THERMAL

TYPE OF SERVICE

• CENTRAL STATION

• COOPERATIVE

• DIRECT CONNECT

• PROPRIETARY

I

36

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