The new UL325 standard (effective August 1, 2018) requires two means of monitored protection — either two external sensors, two inherent means or one external and one inherent — for each entrapment zone.

These monitored photoeyes send a signal to stop and/or reverse operation when sensing an obstruction of the infrared light beam. Photoeyes provide a reliable safety method to protect vehicles as well as people from damage or injury.

There are two styles of photoeyes:
Thru Beam – a two piece unit with a separate transmitter and receiver mounted opposite each other
Retroreflective – a transmitter and receiver in one unit with a separate reflector