US Patent 10287801 Door lock alarm

A door lock alarm includes a housing affixed to a door panel that carries a door lock and is hinged to a door frame, and a sensor including a circuit substrate mounted in the housing, a microprocessor installed in the circuit substrate, a sensor component electrically coupled to the microprocessor to face toward the door lock for detecting the presence of the latch bolt of the door lock in the locking position and providing a corresponding signal to the microprocessor so that the microprocessor activates alarm to give off an alarm signal upon receipt of the signal from the sensor component.