What are the three common causes of sensor failure?

The three most common causes of garage door sensor failure are misalignment, wiring problems, and lens contamination or environmental damage. First, misalignment is by far the number one cause. The sensors are mounted on flexible brackets near the floor where they can easily be bumped by a car, bike, shovel, or even sweeping. Even a movement of a few degrees can break the narrow infrared beam, causing the receiving sensor to blink green and prevent the door from closing. Second, wiring problems are extremely common because the low-voltage bell wire is often stapled to drywall, exposed to attics and garages, and vulnerable to rodents, corrosion, and loose connections at the motor head. A short or break in this wire cuts power to both sensors and causes them to go dark. Third, lens contamination and environmental damage causes failure. Dust, spider webs, dirt, condensation, and direct sunlight can coat or overwhelm the lens. Sunlight shining directly into the receiving sensor can blind it and mimic a blockage. Over time, moisture intrusion from rain or snow melt near the floor can corrode the internal circuit board, leading to intermittent blinking or complete failure, especially on older units.