Most Likely Causes
The two small photo-eye sensors near the floor on each side of the track need to be aligned and unobstructed for the opener to allow the door to close — dust, a spider web, or a bump to one sensor is enough to stop the door. Beyond sensors, a bent track, an obstruction, or an opener's close-limit setting drifting out of calibration can also prevent the door from closing fully.
Why This Is a Security Concern
A garage door that won't close leaves your home exposed, especially overnight. If you can't resolve it quickly by clearing and realigning the sensors, secure the interior door between the garage and your home and treat this as an emergency repair situation.
What to Check First
Wipe the sensor lenses clean, confirm both sensor lights are steady (not blinking), and check that nothing is in the door's path. If the door still won't close, call us with what you've observed.