The Three Beams Detector designed to provide reliable perimeter security both indoors and outdoors. Integrated design, multi installation brackets selectable, the most convenient installation. This Infrared Detector Alarm features unique displacing receiving, transmitting parts with big power & full function checking. The Infrared Detector Alarm also features self-adaption in environment and trouble locking, patented balanced checking, unique digital filtering. The Infrared Detector Alarm with changing frequencies feature can also help cut power consumption to extend the detectors life span.This Photoelectric Detector is suitable to be used in security system in school, home yard, office building ,etc.