NCJ Number
83327
Journal
Security Management Volume: 26 Issue: 6 Dated: (June 1982) Pages: 10-14,16,18
Date Published
1982
Length
7 pages
Annotation
The principles and practical features of passive infrared (PIR) systems for detection of intruders are described.
Abstract
Except for audio intrusion detection systems, PIR is the only major passive detection system available on the market today. In PIR, the intruder is the transmitter and the PIR unit is the receiver. PIR senses motion by dividing the field of view into zones. The PIR detector senses the changes that occur in the field of view when either a cooler or warmer object is introduced. Originally developed in the late 1940's, PIR first became commercially available in the late 1960's. The method is based on the electromagnetic wave theory developed in the 19th century by James Clerk Maxwell. PIR sensors measure infrared radiation by means of thermistors, by the measurement of tiny amounts of current, or by the use of pyroelectric detectors. Most PIR units cost between $125 and $175. PIR systems are immune to most common sources of false alarms. They are not bothered by radio interference, motors, faulty fluorescent lights, and sound. In addition, they are generally immune to vibration, and air turbulence does not bother the most modern units. PIR detectors should generally be used primarily indoors. PIR systems are easy to install and maintain. They are difficult to defeat, except by an extremely knowledgeable intruder. Many PIR detectors are designed to operate from about 20 degrees below zero to 160 degrees above zero Fahrenheit. Diagrams are included.