US Patent 8184004 System to detect presence in a space

A system to detect a presence in a space is provided and includes a sensor to issue a signal at an instance when a door to the space closes, a detector to periodically issue packets that identify when a presence was last detected in the space, and a processing unit, coupled to the sensor and the detector, which is configured to receive the signal and the packets and which has executable instructions stored thereon that, when executed, cause the processing unit to identify when the door closes based on the signal and to judge the space to be unoccupied after a wait time if the packets indicate the presence was last detected prior to the closing.