The Transmitter / Receiver Photo Eye Sensor pair photo eyes have a transmitter photo eye on one end and a receiver photo eye on the other end. The transmitter/receiver photo eye can achieve higher distances. Photo eyes are typically used with swing and slide gates. Photo eyes are invisible beams that stretch across the vehicle lane. If the beam is broken, the photo eye output activates. Photo eyes come in 2 different flavors: reflective and a transmitter/receiver pair. The reflective photo eye uses a reflector to bounce the invisible beam back to the photo eye.