Editing Security alarm (section)

===Passive infrared detectors===
[[Image:Burglar alarm.JPG|thumb|A [[passive infrared sensor]] used to detect motion]]

The [[Passive infrared sensor|passive infrared]] (PIR) motion detector is one of the most common sensors found in household and small business environments.  This sensor does not generate or radiate energy; it works entirely by detecting the heat energy given off by other objects.

PIR sensors identify abrupt changes in temperature at a given point. As an intruder walks in front of the sensor, the temperature at that point will rise from [[room temperature]] to [[thermoregulation|body temperature]] and then back again. This quick change triggers the detection.

PIR sensors designed to be wall- or ceiling-mounted come in various [[Field of view|fields of view]]. PIRs require a power supply in addition to the detection signaling circuit.