The term photoelectric detector (PE), as applied to alarm sensors, refers to a device that receives an infrared optical signal from a light source and converts it into an electrical signal.
While not infrared, a common example is found in the safety beam across the bottom of a door opening for a garage door opener.
The photoelectric detector is comprised of two separate units, a transmitter and a receiver. The transmitter projects a beam, which is detected by the receiver. If the beam is interrupted the receiver will generate an alarm condition.
The beams are focused and can cover long distances. Some of the more sophisticated units have timing delays and sensitivity tolerances to prevent nuisance alarms and are available with heaters to prevent frost from covering the optics.These sensors are used in a verity of applications both indoors and out.