Commercial Grade W/less Doorway Beam Sensor (IR Tx/Rx Refl)A compact entry warning system is designed for use in shops, restaurants, doctors and dentist surgeries etc. to alert you to the entry of customers and visitors. The system consists of a send receive unit which transmits an IR beam across the doorway onto a prismatic reflector mounted on the opposite side. The beam is reflected back to the receiver to complete the circuit. When a person walks through the beam, the circuit is interrupted and this