Safety sensor obstruction or misalignment (10-flash signal)

This is the code most people mean by "garage door opener light blinking": you press close, the door reverses, and the opener's main light bulb flashes 10 times. On LiftMaster and Chamberlain units that ten-flash signal is the safety-sensor alarm — the photo eyes near the floor are blocked, dirty, misaligned, or wired wrong, and the opener won't let the door close over a beam it can't confirm.

It's a DIY fix and free in most cases. Clear the door opening, wipe both lenses, and align the brackets until both sensor LEDs sit steady; the sensors mount about six inches off the floor on each side. Then eyeball the wire run for staple damage. Bring in a tech only if a sensor or the wiring has actually failed. One caveat: some post-2022 boards dropped the ten-flash feature, so on a newer opener a door that won't close but doesn't flash still points at the sensors — read the up/down arrow codes on the motor head instead.