Since 1993, every garage door opener sold in the U.S. has included photo-eye safety sensors — the small units mounted a few inches above the floor on each side of the opening. When they fail, the opener refuses to close the door, or closes it only while you hold the wall button. That behavior is the system protecting you. Here is how to find the fault.
How the sensors work
One unit (the sender) projects an invisible infrared beam across the doorway; the other (the receiver) watches for it. If the beam is broken — by a child, a pet, a trash bin — the opener will not close the door, and if the beam breaks while closing, the door reverses. Each unit has an indicator light: typically amber on the sender, green on the receiver. A solid receiver light means aligned and happy; a blinking or dark receiver light means trouble.
Step 1: Look for the obvious obstruction
Boxes, bins, a shovel, a bike tire, a pile of leaves — anything crossing the beam line near the floor stops the door. Also check for the classics: a spiderweb built across a lens (extremely common), a leaf stuck to the sensor face, or a splash of mud. Clear the path before touching anything else.
Step 2: Clean the lenses
Wipe both lenses with a soft, dry cloth. Dust and cobwebs scatter the beam enough to fault the system even though the path looks clear. While you are there, check that neither bracket has been bumped — a kicked or vacuum-nudged sensor is the most common cause of all.
Step 3: Realign
If the receiver light is blinking, the eyes are misaligned. Loosen the wing nut on the receiver's bracket, and gently pivot the unit until its indicator glows solid — the sender should be aimed straight across at the same height. Tighten the nut without shifting it. If the light flickers as you tighten, the bracket may be bent or the mounting loose.
Step 4: Check the wiring
Sensor wires run from the opener head down to each unit, stapled along the wall and track. Look for breaks, crushed sections (staples driven through the wire are a classic), corrosion at the terminals, and rodent damage. A wire shorted to the track will fault the system intermittently. Wiring repair is safe for careful homeowners with the power off — but if the fault survives a wire check, the sensors or the opener's board need a technician.
Step 5: Read the opener's blink code
Most openers flash their lights a set number of times to report the fault — ten flashes is the classic sensor code on many brands. Count yours and note it; telling us the pattern when you call for repair genuinely speeds the visit.
What never to do
Do not tape, jumper or disconnect the sensors to "fix" the annoyance. The photo-eyes exist because garage doors seriously injured children before they were required. A door that closes with defeated sensors is a liability in every sense. If the sensors are dead and the parts are obsolete, a modern opener restores full protection along with better security. And if the door was forced closed by holding the wall button — a built-in override — treat it as a temporary measure only, and get the sensors fixed. During a tune-up, we test sensors and auto-reverse on every visit, so faults get caught even when the door seems to work.
Sunlight, the sneaky sensor fault
One more cause worth knowing: direct sun. If your door refuses to close at the same sunny hour each day but behaves at night, low sunlight may be flooding the receiver's lens and blinding it. The tell is the clock-like pattern. Shading the receiver with a short cardboard hood (fitted so it cannot cross the beam) or swapping the sender and receiver positions often cures it — and a technician can fit a proper sun shield during a visit. It is a small fault, but a perfect example of why sensor problems deserve diagnosis rather than defeat.