Garage Door Safety Sensors: How They Work and Why They Matter
Garage door photo eye safety sensors send an infrared beam across the opening about six inches above the floor. If the beam is broken while the door is closing, the door stops and reverses. They became mandatory on new openers in 1993, and an opener without them has no reliable way to stop for a child or a pet.
What they are
Two small units mounted on the track brackets near the floor, one on each side of the opening. One transmits an infrared beam, the other receives it.
While the door is closing, the opener watches that beam. Break it and the door stops and reverses immediately.
They exist because garage doors have killed children. Federal rules in the United States made an entrapment protection system mandatory on residential openers manufactured after January 1993, and photo eyes are how essentially every manufacturer implements it.
Mounting height matters more than people think
Six inches above the floor, maximum.
The reason is specific. A child lying down or crawling under a closing door, or a pet asleep in the opening, is low. Sensors mounted at knee height look impressive and protect nothing at the height where the risk actually is.
If yours are mounted higher, move them down. It takes minutes.
How to align them
Each sensor has an indicator light. Behaviour varies by brand, but almost universally:
- Steady light on both: aligned and working
- Flickering or dark on one: not aligned, or the beam is blocked
- No light at all: no power to that sensor, usually a wiring fault
To align, loosen the wing nut on the bracket, move the sensor slowly until the light goes steady, and tighten it without moving it. If you cannot get a steady light, check for cobwebs on the lenses, something on the floor breaking the beam, or damage to the wire.
The two things that break them
The wire. It runs along the wall at floor level, which is exactly where it gets caught by bikes, stapled through during other work, and chewed by rodents. Look for damage before assuming the sensor is dead.
Sunlight. Low direct sun into the receiving lens washes out the beam. If your problem happens only at a particular time of day and your garage faces the sun, that is why. A small shade over the sensor fixes it.
The reversal test
Sensors are not the only protection. The opener also monitors resistance, and it should reverse if the door meets an obstruction.
Test it: lay a length of timber flat on the floor in the opening and close the door onto it. The door should touch, stop and reverse.
If it does not, the down force is set too high. That setting exists to be adjusted, but it should be adjusted properly, because an opener with the force turned up is an opener that will keep pushing on whatever is under it.
Run this test twice a year alongside the balance test.
If your opener has no sensors
It was made before 1993, which means it is over thirty years old. Parts almost certainly are not made for it any more, and it has no automatic way to stop for a child or a pet.
Replace it. A new opener is $281 to $630 installed, and on a unit that age it is not a repair decision, it is a safety one.
Related questions
How high should the sensors be mounted?
No more than six inches above the floor. Higher, and a small child or a pet lying under the door can be below the beam entirely, which defeats the purpose.
Can I bypass the sensors permanently?
Most openers let you close by holding the wall button continuously, which is intended for one-off use when a sensor has failed. Disabling them permanently removes the only automatic protection the door has.
My sensors are fine but the door still reverses. Why?
Then it is the down force setting or the down travel limit. The opener is meeting resistance it interprets as an obstruction, either because the limit sends the door too far into the floor or because something is binding.