A beam break sensor is a form of occupancy sensor that uses a beam of light to determine whether or not something is between the two sensors. These types of sensors are used in everything from automatic garage doors and alarm systems down to simple wheel encoders.

This particular sensor projects a beam of infrared light which can be picked up by the matching infrared sensitive receiver. These are far more accurate at determining occupancy of a specific location when compared to a PIR sensor. When the beam is blocked, the receiver will change state and read by a microcontroller or used to trigger a relay or other device.

When powered with 5VDC the sensor has a range of up to 50cm, at 3.3V the range will be reduced. The receiver is an open collector transistor, and can sink up to 100mA current. If you wish to read the receiver using a microcontroller a pull up resistor will be required on the signal wire. To make these as easy to use as possible to use, both the emitter and receiver are housed in a small plastic case with mounting hole.