What does a blinking light on a garage door sensor mean?

A blinking light on a garage door sensor means the receiver is not getting a clean continuous infrared beam from the sender, so the opener treats the path as obstructed and refuses to close the door. The most common causes are misalignment from a bumped sensor, dust or cobwebs on the lens, an object sitting partway in the beam, sun glare hitting the receiver during certain hours, or a loose or pinched wire running back to the opener. Start by wiping both lenses, clearing the path, and gently rotating the green receiver until the LED stays solid. If the blinking continues after alignment and cleaning, check the bell wires for staples or damage, then swap sensors left-to-right to identify a failed unit.