KERUI 2 Beams Indoor 300m Outdoor 100m Photoelectric Home Security Alarm Infrared Detector Sensor This is Alarm Two Beam Photoelectric Infrared Detector ABT- 100m. Install them at the opposite positions. Then there is a infrared area between these two detector parts. When someone passes the infrared region for an adjusted response time, the detector will send alarm signal to the security alarm host (which not included here) work with 2pcs power apater Integrated design, installation brackets, the most convenient installation. Holographic spot real-time report. Unique displacing receiving, transmitting parts with big power. Full function checking, self-adaption in environment and trouble locking. Patented balanced checking, unique digital filtering. Some red and green LED indicator lights are fixed. PS : Not all the beam Detector can work with your alarm system,please let me know what kind of alarm system in your hand before you order. It must work wit the alarm system. Great to be installed for security system in school, office building, hospital, home yard, etc.