US Patent 7456738 Transport refrigeration door status sensing device

A door status sensing device for a transport container including a door. The door status sensing device includes an emitter attached to the container that transmits a first wireless signal in a first direction toward the door. A reflector attaches to the door and is aligned with the emitter to receive the first wireless signal, and generates a second wireless signal in a second direction opposite the first direction in response to the first wireless signal. The sensing device further includes a receiver attached to the container adjacent the emitter and opposite the reflector. The receiver is substantially aligned with the reflector, receives the second wireless signal, and generates a third signal indicative of the condition of the door condition in response to receipt of the second wireless signal. A controller selectively generates an alarm in response to the third signal indicative of the condition of the door.