Anti-theft warning device

摘要

The device is operated by a security tag attached to the protected item, to provide an acoustic and/or optical signal upon attempted removal of the item from a protected area. The security tag incorporates a printed circuit acting as an open oscillator circuit, stimulated upon proximity to a transceiver which switches periodically between transmitter and receiver modes. The residual energy from the oscillator circuit is transferred to the receiver and evaluated for operating the alarm. An optical or acoustic alarm device may be incorporated in the security tag, with a timer for limiting the alarm signal duration.