IR transmitter and IR receiver 18 x 9 x 20 mm. An infrared beam sensor consists of a transmitter which sends out invisible IR (infrared) light-beams and an IR receiver registers this light. In the presence of obstacles this triggers the receiver and then a control unit (not included). e.g. Busch 5963 Timer electronic relays 5740, 5743 or timer switch control module 5745.