The sensor above an automatic sliding glass door uses motion or presence detection to open the door and to stop it closing on someone standing in the doorway. A sensor that misses people, triggers randomly, or stops responding is usually dirty, misaligned after a knock, or has a failing connection to the control unit; direct sunlight or reflective flooring can also confuse some sensor types.
We clean and realign the sensor first, then check its wiring and settings at the controller, and replace the sensor itself only if it still will not detect reliably.