Why is one garage sensor blinking red?

One garage sensor blinking red is a diagnostic signal that usually indicates a wiring or power issue on the sending side, especially on Genie and Overhead Door systems. The sensor with the red light is typically the sender that projects the invisible infrared beam across the garage floor. When that red light blinks instead of staying solid, it means the sensor is not getting consistent low-voltage power from the garage door opener motor unit, there is a loose wire connection, or there is a short in the bell wire that runs along the ceiling and down the wall. Check where the wires connect to the motor head terminals, often labeled white and grey, and make sure they are tight and not corroded. Also look for staples that have pierced the wire, rodent chewing, or damage from a ladder. Less commonly, a blinking red can mean the sensor board itself has failed due to moisture, age, or a power surge. Try unplugging the opener for 30 seconds to reset it. If the blinking continues after checking wires and cleaning the lens, the sensor unit likely needs replacement. Do not confuse this with a blinking green receiver, which means misalignment.