What they are and why the door obeys them
Look at the bottom of each vertical track. You will find two small plastic eyes facing one another across the doorway, wired back to the opener. One sends an infrared beam, the other receives it. Break that beam while the door is closing and the opener stops and reverses.
They are not an optional convenience. Photo eyes have been required on residential garage door openers sold in the United States since 1993, and the height they are mounted at — no more than six inches above the floor — is set deliberately, so the beam catches a child or a pet before the door reaches them.
The five-minute check, in order
1. Clear the line between them
Anything crossing the beam stops the door: a bin that has drifted, a bike wheel, a bag of mulch, a coiled hose, a broom that has slid down the wall. Move it, then try again.
2. Wipe both lenses
A dry cloth on each lens. In Georgia the two reliable culprits are spring pollen, which films the lens over, and spider webs — a single strand strung between the eye and its bracket is enough. Late March is our busiest stretch for doors that suddenly stop closing with nothing visibly wrong.
3. Read the LEDs
Each eye has a small indicator light. What you are looking for is one steady light on each. Interpret it like this:
- Both steady — the beam is good. The fault is elsewhere; skip to the last section.
- One flickering or dim — alignment. Go to step 4.
- One completely dark — power or wiring to that sensor, not alignment.
4. Realign
Loosen the wing nut on the bracket of the sensor whose light is unhappy, and move it in very small amounts — a millimetre at a time — until the light goes solid. Then tighten the nut without letting the sensor rotate as you do it, which is the step most people lose the alignment on. Check the bracket itself has not been knocked or bent; a bumped bracket is the most common way alignment goes in the first place.
5. Follow the wire
Sensor wire is thin bell wire, usually stapled up the wall and along the ceiling to the opener. Look for a staple driven through the insulation, a mouse chew, a wire pulled loose from a screw terminal on the opener head, or a splice that has corroded in a damp garage. A dark LED with clean lenses points here.
The afternoon-sun problem
If the door closes fine every morning and refuses from about three o'clock, nothing has broken. A doorway facing roughly west lets low sun shine directly into the receiving eye and swamp the infrared beam it is looking for. It is worst in autumn and winter, when the sun sits lowest.
Two fixes, both permanent: a small shield or hood over the receiving lens, or swapping which side the sending and receiving eyes are mounted on so the receiver faces away from the street.
How to prove it is the sensors
Press and hold the wall button rather than tapping it. On almost every opener made since 1993, constant pressure on the wall button bypasses the photo eyes, and the door will close for as long as your finger stays down. If it closes that way and will not close any other way, the sensors are confirmed as the fault.
When the sensors are fine and the door still won't close
Both LEDs steady, lenses clean, nothing in the way — then the beam is not your problem. The next suspects are the close-limit setting, which makes the door reverse the instant it touches the floor, and the down-force setting, which makes it reverse partway. A dent in the track or a binding roller will do it too. Our full won't-close checklist works through all of them in order.