US Patent 7561039 Transmitting unit

A transmitting unit includes a transmitter for transmitting signals of coded information about a position close to the unit in a space substantially unreachable by a satellite-based navigating system so as to provide a receiver arranged on a moving object present in the space with the position information for determining the position of the object. The transmitter is adapted to normally be in an inactive non-transmitting state, and the unit further includes a detector adapted to detect movement of an object within a space and activate the transmitter to transmit signals only when movement of an object in the space is detected.