Install each pair at the opposite positions.Then there is a infrared area between these two detector parts. When someone passes the infrared region, the detector send Report signal to the security Report host (which not included here). Great to be installed for security system in school, building, hospital, home yard, etc. When interrupt the infrared, the relay output switch signal, it can work for parking barrier, walking gate, vehicle gate as body induction. It also can work as window, door and passageway anti-burglar detection. Detecting range can be reduced to 30% in bad weather conditions, like rain, dust, etc., Weight: 0.24471311082 pounds, Manufacturer: Frewurwer