Blinking lights on the small boxes by the floor mean the safety sensors cannot see each other. Usually they are dirty or knocked out of line, and the door will not finish closing until they are steady. One light is steady. The other blinks. You hit close and the door climbs back up.
Those are the safety sensors. One sends a beam. The other catches it. When the beam is solid, both lights usually sit steady the way the sticker says they should. When something blocks the path, or the eyes think something does, the blinking starts and the opener refuses a full close. That is the feature working. A bike, a kid, a trash can. The reverse stops a crush.
If one light stays solid and the other blinks
That is the classic misalign or dirty receiver pattern. Wipe both lenses with a soft dry cloth. Do not soak them. Look at the LEDs while someone stands clear of the door. If one stays dark or keeps blinking, loosen the wing nut a touch and nudge the box until both settle to solid. Tiny moves. You are aiming the lenses at each other, not rebuilding the track. Power stays on. Hands stay off the moving door.
Dust, a cobweb, wet leaves after rain, or a storage bin that drifted an inch into the beam will trip the same blink. A broom that bumped a bracket so the eyes no longer stare straight is just as common.
If both blink or both stay dark after you wipe
Dirt alone is less likely. Check the path is clear. Look for a loose wire at the eye or along the wall. Make sure the opener has power and the eyes get feed. Low sun late in the day can hit one lens so hard the receiver freaks out even when the glass looks clean. Shade the lens with your hand. If the blink settles only then, sun glare is the culprit. If both stay dark after a wipe and a gentle aim, stop twisting brackets. Wiring or a failed pair needs a shop.
If the lights look solid but the door still reverses mid close
Then the problem may be binding higher up. A sticky roller. A bent track. Weather seal dragging on the slab. The opener feels a hard stop and treats it like a beam break. If the door reverses only after it kisses the floor, read the close then climbs back up note. That fork is often travel limit or force, not dirty lenses. If the door hangs with a strip of daylight under the seal, see the stops short note instead.
Pull the emergency release only if you need a car out and the door still feels even by hand. The steps match lifting the door by hand when the power is out. Move it slow from the side. If it lists, scrapes, or feels like a brick, leave it. Use the house door. Do not stand under a hanging panel.
What it is not
This is different from a remote that does nothing while the opener stays quiet. Silent remotes are often batteries, lock mode, or a power cut. Blinking eyes with an opener that tries to move means the motor is alive and the safety circuit is unhappy.
It is also different from a broken torsion spring. A spring snap leaves the door dead heavy with a bang you heard earlier. Sensor blinks do not come with that bang. An opener that hums or grinds like gravel is a drive or balance problem up at the head. Here the complaint lives at the floor eyes.
What not to do
Do not stand under the door while you aim the eyes or test a close. Do not soak the sensors with a hose or spray cleaner into the housings. Do not force close past a reverse by holding the wall button down just to park the car. That defeats the safety circuit. Do not keep cycling while one eye blinks.
I am not a contractor. This is just what shows up when the lights by the floor will not stay solid and the door refuses to finish a close. A shop that works on garage doors will clean the lenses, realign the brackets, and check the track in one visit instead of you guessing which blink pattern means what.
Manufacturer safety tips for photo eyes and reverse live on DASMA's garage door opener page. Those notes cover sensors near the floor and the six inch reverse rule.
The U.S. CPSC garage door operator page covers federal rules for automatic openers. Blinking eyes that refuse a close are that safety circuit talking.
If the sensors keep blinking and you want someone local to look, get a quote.