Abstract: The present invention is a fiber optic security system for protecting expensive equipment from tampering or theft. The fiber optic security system comprises an emitter for generating signals, a detector connected to an alarm for monitoring the signals and a sensing coupler or photon switch of novel design which is easily mounted to each piece of equipment that requires protection without defacing the equipment. The sensing coupler mounts the tips of optical fiber ends in a position aligned along a single axis to allow light generated by the emitter to pass through. Any attempt to remove the sensing coupler causes the tips to be misaligned and the light to be deflected. This causes an optic path interrupt and causes the detector to trigger an alarm.