The invention concerns a method of operating a security device in which light pulses are generated by a pulse emitter (3) and directed along a transmission path (5) towards a receiver (7). Power consumption and safety against tampering are significantly improved by virtue of the fact that the receiver output signal is used to prevent pulses from being emitted. Emission of pulses by the emitter (3) is preferably retarded with respect to the occurrence of the receiver output signal. Also described is a security device operated by the method proposed.
