Abstract: A security system for detecting and signalling the presence of abnormal security or hazardous conditions, such as unauthorized entry, glass breakage, fire, smoke, high water level, in individual units, such as a boat, a recreational vehicle, an automobile, which are located or stored in a given security area.. The security system comprises sensor units which, when actuated, transmit coded signals through the atmosphere which identifies each sensor unit and the individual unit on which it is located. A receiver on the individual unit recognizes only the coded signals from sensor units which are on the same individual unit as the receiver. A coded output signal is provided to a slave transmitter on the individual unit which identifies the particular sensor unit which was actuated. The slave transmitter provides a coded transmission signal to a local security station which identifies the particular sensor unit which was actuated and the individual unit where the actuated sensor unit resides.