commgrp@silver.ucs.indiana.edu (BACS Data Communications Group) (12/02/90)
A friend's wife bought a dress from a store which uses electronic anti-shoplifting tags. Not only did the clerk fail to remove it, but it did not trip the alarm when she left. It's a thick white plastic device. Being a true electronics person, my friend dissected it. He found a coil which absorbs energy from an external exciter, which is then rectified and used to power a one- transistor oscillator on a different frequency. He damaged the device during the inspection and could not determine frequencies, but believes that the output is LF, perhaps around 200 kHz. We joked about what fun it would be to lurk near the store exit with a concealed oscillator, but decided that the exciter is probably modulated and the alarm receiver uses synchronous detection, which would be an easy way to reduce false alarms. Anybody know details of these gadgets? -- Frank Reid reid@ucs.indiana.edu