Double-end fiber optic security system for sensing intrusions

A security system is disclosed for detecting intrusions at a plurality of predetermined locations having moveable closure members. The system comprises a plurality of intrusion sensors disposed at the locations for detecting movement of the closure members. Primary and secondary optical fiber sensor lines are routed through the intrusion sensors, and primary and secondary scanning units pulse signals along the sensor lines and receive reflected signals back from the sensor lines. A processor processes the reflected signals to determine if a reflection and/or attenuation change has occurred in a reflected pulse signal signifying a prescribed level of unauthorized intrusion activity which matches a signature intrusion signal. In the event of a cut through in the sensor lines, the primary sensor line monitors the sensors downstream of the break, and the secondary sensor line is activated to monitor the sensors upstream of the break.