The core component of the passive infrared device is an infrared detector (infrared sensor). Through the cooperation of the optical system, it can detect the change of thermal radiation in a certain stereo space. When there is no target such as a moving body in the prevention area, since all background objects (such as walls, furniture, etc.) have relatively small infrared radiation energy at room temperature and are basically stable, all alarms cannot be triggered. When a human body moves around the detection area, it will cause a change in the energy of the infrared heat radiation. The infrared sensor converts the received infrared heat radiation energy between the active human body and the background object into a corresponding electrical signal, and after appropriate processing, sends it to the alarm controller to issue an alarm signal. This product adopts the detector of all digital CPU processor and advanced fuzzy logic control technology to ensure the detection range and enhance the stability and anti-RF, strong light interference and other characteristics. The built-in sensitivity selection function and temperature compensation circuit ensure the detection distance in different temperature environments to avoid false alarms caused by environmental interference.