A photo eye is a transmitter and receiver pair, typically mounted at 600 to 800 mm height on each side of an automated gate's path. The transmitter sends a continuous infrared beam to the receiver. As long as the beam is unbroken, the gate can move freely. Break the beam (a person, vehicle, or pet) and the motor's safety circuit triggers, either stopping the gate or reversing its direction depending on the safety logic.
Residential automated gates need at least one photo-eye pair across the opening. Commercial gates usually carry two pairs: one outside and one inside, so the gate is safe in both directions of travel.
Most photo eyes are mains-powered through the motor's safety circuit, but solar-and-battery wireless pairs (like CAME's DELTA-S) are common where running cable across the driveway is impractical.