Photo eyes (safety sensors)
Photo eyes are a pair of infrared sensors mounted on each side of the garage door opening, about six inches above the floor. One projects an invisible beam; the other receives it. Anything interrupting the beam while the door closes triggers an immediate stop and reversal — the primary entrapment protection on every modern opener.
How the beam protects, and where it came from
The physics is a tripwire made of light: an infrared LED on one side, a phototransistor on the other, and opener logic that treats any beam interruption during closing travel as a person in the opening. The response is not a pause but a full reversal to open — and openers refuse automatic close commands entirely while the beam is down, falling back to the constant-pressure wall-button mode. Mounting height is standardized low, near six inches, specifically to catch small children and pets that higher placements would miss.
The history explains the hard line technicians take. Federal safety requirements — UL 325 — made photoelectric protection effectively mandatory on residential openers manufactured from 1993 onward, following documented child entrapment deaths under doors whose force-reversal systems alone proved insufficient. That is why a pre-1993 opener without eyes is treated as end-of-life hardware regardless of how well it runs, and why no legitimate service visit leaves a bypass in place.
Reading the fault, fastest first
| Symptom | Likely cause | The fix |
|---|---|---|
| Receiver LED blinking | beam misaligned or blocked | clear the path, loosen the wing nut, re-aim until steady |
| Fault only at certain hours | direct sun flooding one lens | shade test confirms; hood or emitter-side swap retires it |
| Both LEDs dark | power or wiring break | check the low-voltage run for staples, kinks, disconnections |
| Intermittent after rain | moisture in a lens housing | dry, reseat, replace the pair if it recurs |
| Fault after a bump | bracket knocked out of aim | the wing-nut realignment — the classic ten-minute fix |
What owners should know cold
This is the legitimate DIY zone
Alignment, lens cleaning and wire inspection are homeowner work by design — low voltage, floor level, LED-verified. The eyes are the one safety component built to be user-serviceable.
The monthly test takes one minute
Start the door closing and wave a broom through the beam path: immediate reversal is a pass. Pair it with the 2×4 reversal test and the balance test for the full safety trio.
Wiring is the hidden failure mile
The thin sensor wires run stapled along walls and ceilings for twenty-plus feet — every staple is a future short. Intermittent faults with clean, aligned lenses usually live in that run.
Replacement is cheap; test after
A new sensor pair is an inexpensive part on a service visit. Whatever the fix, the close-out is non-negotiable: an observed automatic close plus a beam-break reversal, passed in front of you.
Photo eye questions
What do the little lights on each sensor mean?
They are the diagnostic interface. Typically the sending eye holds a steady light whenever powered, while the receiving eye lights steadily only when the beam lands cleanly — blinking or dark on the receiver means blocked, misaligned or miswired. Brands vary the colors, but the logic is constant: two steady lights, system healthy; anything else, start with the lens-and-alignment ritual before suspecting wiring.
Why will the door close when I hold the wall button but not from the remote?
That asymmetry is designed, and it is diagnostic. Remotes command an automatic close, which the opener refuses while the eyes report a fault; the wall button held down is a constant-pressure close, permitted because a human is standing there watching. If the hold-to-close works while the remote fails, the eyes are your fault source — usually alignment, sun glare or a cobweb rather than electronics.
Can I just bypass the sensors to make the door work?
Taping a lens, jumping the wires or relocating both eyes to face each other at the motor head all disable the entrapment system — on a machine that closes with enough force to injure. Every bypass converts a ten-minute alignment fix into a standing hazard for every person and pet in the household. The correct responses to persistent eye faults are realignment, rewiring or replacement — a sensor pair is an inexpensive part.