A slot sensor, also known as a slot photoelectric sensor or slot photo interrupter, is a type of sensor that detects the presence or absence of an object by using an infrared (IR) light source and a receiver in a slotted configuration. It consists of an emitter and a receiver placed on opposite sides of a slot or gap. When an object interrupts the infrared beam between the emitter and receiver, the sensor detects the interruption and provides an output signal.