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 will send Report signal to the security Report host (which not included here). When interrupt the infrared, the relay will 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. Great to be installed for security system in school, office building, hospital, home yard, etc. Detecting range can be reduced to 30% in bad weather conditions, like rain, dust, etc. Detector Area: 20m work voltage:12V,24V AC DC temperature: +60°C- (-20°C) Water Proof, UV proof Color: As Shown Material: Plastic+Electronic Component Package Contents: 1 x Infrared receiver 1 x Infrared projector