Detection system protecting goods in shop from theft - uses two passive signals indicating passage through EM field and active signal also indicating unauthorised removal and discharged battery

摘要

The detection system reacts in two different ways to the passage of an object through its electromagnetic field. Firstly, it produces a passive feedback message. Secondly, it responds in an active way by sending a second signal, pref. electromagnetic. The second signal is activated by the electromagnetic field from the system and is detected by a second receiver. An alarm is triggered by both this receiver and by the first detection arrangement. The second signal is also emitted if the detection system is interfered with by attempting to remove the detector from the goods being protected. The second signal is further emitted when the battery needs recharging. In this state optical and acoustic signals are also produced to alert the user.