Do garage door sensors need to be perfectly aligned?

Yes, garage door sensors need to be fairly precisely aligned to maintain an uninterrupted infrared beam between them, but they do not need to be perfectly aligned to microscopic tolerance, as they have some tolerance built in. The sensors, also called photo-eyes or safety eyes, are mounted on each side of the garage door about 4 to 6 inches above the floor, one sending an invisible infrared beam to the other receiver. If they are misaligned even slightly, the receiver cannot see the beam, and the opener will not allow the door to close, or the door will close partway and then reverse, with the receiver LED flashing or turning off. You need to align them so they point directly at each other, with lenses facing each other at same height. To align, loosen the sensor bracket wing nut, adjust sensor up, down, or sideways until the green receiving light becomes steady, not flashing, then tighten bracket without moving sensor. Brackets can get bumped by foot, shovel, or car, causing misalignment. Vibration from door operation can also loosen brackets. Sensors should have solid mounting. They do not need to be level to ground perfectly, but must face each other. Keep lenses clean, remove spider webs, and ensure no direct sunlight hitting receiver causing false blockage. Proper alignment ensures safety auto-reverse works and prevents accidents.