The sensors send an invisible beam across the bottom of the opening. If anything breaks that beam while the door is coming down, the opener stops and reverses. That is the whole job, and it is why a pair of sensors Sumo Garage Doors prices at $30 to $90 as a part can keep the car parked in the driveway until they are fixed.
Why every opener has them
The rule goes back more than three decades. In December 1992 the federal safety commission, the CPSC, published its final rule after counting 54 deaths of children between two and fourteen, all trapped beneath automatically opened doors, in reports going back to 1982. Any residential opener built from 1993 on has to protect against entrapment, and the industry standard behind it is UL 325.
DASMA’s look back at the standard, written for its 50th anniversary in 2023, says the 1991 edition of UL 325 approved photo eyes and edge sensors as external entrapment protection, and the CPSC rules made monitored protection such as a photo eye system mandatory on openers made or imported after January 1, 1993. DASMA reports that child entrapment deaths or serious injuries on properly installed doors with photo eyes have been nearly eliminated.
So the sensors are not optional, and an opener that will not close until they see each other is doing exactly what the law asks.
Reading the two lights
Chamberlain, which makes both its own and LiftMaster openers, says the sending eye carries an amber light and the receiving eye a green one. Both should glow steady. Ten flashes of the main opener lights is its signal that the beam is broken or the eyes no longer face each other.
| What you see | What Chamberlain says it usually means |
|---|---|
| Amber steady, green off or flickering | Receiving eye is out of line or blocked. Faulty sensors and broken or shorted wires are also possible. |
| Both steady, door still flashes and reverses | Something else, often a setting on the opener. Sumo Garage Doors points to the close limit. |
| Opener shows 1 up, 1 down flash | Sensor wires cut or not connected |
| Opener shows 1 up, 2 down flashes | Sensor wires reversed or shorted |
Checks Chamberlain lists for owners
- Take away whatever is sitting between the sensors. Both lights should come on steady.
- Loosen the wing nut on the green sensor, aim it at the amber one until the green light glows steady, and tighten it again. If it still blinks, do the same with the amber one.
- Watch for sun. Chamberlain says sunlight shining into the receiving eye can drown out the beam, and the opener then acts as if something is in the way.
- Check the wires at the sensors. Chamberlain says white goes to the white terminal and white with black stripe to the black one, and a gentle tug tells you whether they are secure. Pre-wired garages may use other colors.
If none of that brings both lights on steady, Chamberlain’s next steps are testing the wire run and the sensors themselves, which ends in replacing one or the other. That is where a call to a company makes sense.
Until it is fixed, Chamberlain says older openers can close the door if you press and hold the wall control push bar until the door reaches the floor. That override is not on openers or replacement logic boards made after February 3, 2022.
Sensor repair prices on Long Island
| Job | Price | Source |
|---|---|---|
| Realign or replace the pair | $85 to $200 | Sumo Garage Doors, Westbury (Aug 2026) |
| Replacement sensors, part only | $30 to $90 a pair | Sumo Garage Doors |
| Small adjustments and sensor work | starting near $120 to $180 | Expo Garage Doors, Roslyn (Oct 2026) |
| Diagnostic visit | $50 to $150, often applied to the bill when you go ahead | Sumo Garage Doors |
Ask whether the price covers a new pair or only realigning the old ones, and whether the tech will replace the wire run if that turns out to be the fault.
When it is not the sensors
If both lights glow steady and the door still refuses, the trouble is in the opener or the door. Start with opener repair for flash codes, logic boards and travel settings, or the repair page if the door itself sticks or drags.