The Mighty Mule photo eyes are a non-contact photoelectric safety device for your gate opener that prevents the gate from closing when an obstruction is in the path of the beams. This safety feature is easy to install on the inside and on the outside of your gate. For a typical pull-to-open application, two PHOTO EYES would be placed across the driveway from each other just outside of the gate, and two more would be placed on the inside of the property just outside of the reach of the gate in its open position. These sensors do not allow the gate to close when it senses any obstruction (vehicle, person, horse, etc.) in the path of the beam.