PIR Motion Detector Sensors For Your Home Security Alarm System
PIR (Passive Infrared) motion detector sensors are one of most popular type alarm
sensors due to their cheapness and reliability. There are used to detect movement
within the range of the sensor and virtually all burglar alarm systems are sold
with at least one of these devices in the kit.
Infrared motion detection has been around for a number of years and this passive
system basically works on the principle of detecting a change in temperature over
time using infrared energy. To detect a person, the sensor is designed to emit the
correct infrared energy in order to pick up human body temperature. As a person’s
skin temperature is around 93 degrees Fahrenheit, a wavelength between 9 to 10 micrometers
of infrared energy is required.
This type of sensor will not trigger if the person is standing still as the sensor
is looking for a change in temperature – within a few seconds or so. When a person
walks in the range of the sensor the amount of infrared energy changes rapidly and
is easily detected.
So what about when the sun goes down, or it goes darker outside due to the weather?
This is a change in temperature too so wouldn’t it set the alarm off? Well, as the
sensor is designed to only detect rapid changes in temperature – over a few seconds
– a very slow change in temperature will not set the alarm off.