|GTO R4222 PhotoEye - PhotoBeam - Obstruction Sensing Device. GTO PRO R4222 Photo Beams - Through Beam - 12v - Non Contact System. Safety Photo Beams For Gate Openers. The GTO photo eyes are a valuable safety feature that will keep the gate from closing when any obstruction is in the path of the photoelectric beam. The photo eyes use Dual Beam and Through Beam technology, which are more reliable than reflective beams because they do not allow sunlight to create a false reading .