From: David Arney
Subject: arphid tagging vs. sensormatic
Date: November 17, 2004 9:31:54 PM CET
To: Bruce Sterling
Hello,
I thought you'd be interested to know that the tag on that lovely bottle of hooch isn't actually RFID, but a lowly sensormatic acoustomagnetic tag. Sensormatic is pushing arphids, but they probably haven't made it into the liquor stores yet. Give it a few years...
The key difference is that these tags just trip an alarm when you carry them through the sensor field. There's no unique ID and the tags are used in many products (most new DVDs, for instance), so they'd be pretty useless for identifying or tracking customers or merchandise.
(((I see.)))
If you pop one of the sensors open, there are two strips inside. One of them is magnetic and the other is a fancy material which changes size in response to magnetic fields. When the tag is hit by the ~60 Hz radio wave from the sensor, it starts to resonate and continues to wiggle even after the radio signal stops, becoming a transmitter. The sensors by the door pick up this weak transmission and sound the alarm. Incidently, these metallic strips are perfect for shimming locks so keep them in mind next time you need to rekey a door. :)
(((Look at the many benefits of having a
technically aware readership!)))
Here's sensormatic's site on these tags:
http://www.sensormatic.com/EAS/labels/default.asp
And a site which describes in more detail how they work:
http://www.phonelosers.org/wal-mart/security_tags.html
-Dave Arney
Systems Design Research Lab
University of Pennsylvania
