Security tag with tell-tale capability

The security tag includes a read/write RFID transponder and an optical comparitor. The optical comparitor includes a light source 1, a scrambler block 2, connected via a light-pipe 3 to an array of sensors 6, the output of which is analysed by a microcontroller 12. The light-pipe 3 passes through the locking device to be protected. A second system 11 transmits the encrypted results of, single use, randomly chosen optical experiments carried out by the comparitor each time the RFID tag is checked. The tag may be mounted inside or outside the device to be protected. If the light-pipe is damaged the results of the optical experiment defined by the current RFID tag number will be different from the initial result encrypted in that number and the RFID reader will be alerted via radio device 11.