QUICK ANSWER
A blinking light on your opener or a door that reverses before it closes almost always means the two safety sensors near the floor have lost their line of sight to each other. It’s one of the most common calls we get, and one of the easiest to fix yourself if you know where to look. Here’s what the blinking actually means and how to clear it.
What the Sensors Actually Do
Every opener made since the mid-1990s has two small sensor eyes mounted about six inches off the ground, one on each side of the track. They shine an invisible infrared beam between each other, and if anything breaks that beam while the door is closing — a stroller, a pet, a stray box — the door reverses instead of coming down on it. If that beam is blocked or misaligned even when nothing is in the way, the opener treats it the same as an obstruction and refuses to close, usually with a blinking light on the motor unit as the tell.
The Usual Culprits
- Something’s in the way. Check for a broom, garbage can, garden hose, or shoveled snow sitting between the two sensors — it doesn’t take much to block the beam.
- Dirty or fogged lenses. Dust, spiderwebs, or condensation on the sensor lens can weaken the beam enough to trip a false reading. Wipe both lenses with a dry, soft cloth.
- Misalignment. A bump from a parked car, a bike, or just settling over time can knock one sensor’s bracket out of position. Both sensors should have a small indicator light — usually one solid, one blinking when they’re not aligned. Loosen the wing nut on the bracket and gently adjust the angle until both lights go solid.
- Direct sunlight. On garages that face east or west, low morning or evening sun can shine directly into a sensor’s lens and overpower the beam. If it only happens at certain times of day, this is often the reason — a small shade or angling the bracket slightly downward usually solves it.
If the Lights Are Solid and It Still Won’t Close
If both sensor lights look solid and aligned but the door still reverses or won’t close, the problem has likely moved past the sensors themselves. A cut or corroded wire running to one of the sensors, a failing circuit board in the opener, or an unrelated mechanical issue with the door binding on the track can all produce the same symptom. That’s where it stops being a five-minute fix — see our guide on garage door won’t close all the way for the other causes, or our opener repair page if it looks like the opener itself is the issue.
What Not to Do
Don’t disconnect or unplug the safety sensors to force the door closed. It’s tempting when you’re in a hurry, but those sensors are the only thing stopping the door from closing on a person, pet, or car — bypassing them is a real safety risk, not just an inconvenience. If holding down the wall button in “manual hold” mode is the only way to get it closed, that’s a sign to get the sensors properly fixed, not a workaround to live with.
Frequently Asked Questions
Why does my door open fine but won’t close?
That’s the classic sensor symptom. Openers only check the safety sensors when closing, not opening, so a blocked or misaligned sensor lets the door go up normally but stops it from coming down.
Both sensor lights are on, but one is red and one is green — is that a problem?
Colors vary by brand, so it’s normal for the two sensors to look different from each other. What matters is whether both show a steady light rather than blinking or off — check your opener’s manual for what your specific brand’s steady state looks like.
Can I replace a sensor myself?
If cleaning and realigning doesn’t fix it, a failed sensor unit can be swapped, but it needs to be wired correctly and matched to your opener. Most homeowners are better off having it done right the first time than troubleshooting a wiring issue in the garage ceiling.