It's like a normal rfid sticker, but modified to not respond to any rfid signal unless it has the correct signal.

You inset it into a valuable product, then you register it with the police. As soon as it enters a pawnshop, the pawnshop owner is able to check if it is stolen by querying the device with a list of know stolen items.

If the rifd detects that it's id is called, it replies. Otherwise it stays silent.

This preserves a bit of privacy for the owner, while also allowing the owner to drastically make the product harder to sell to a pawnshop.
-- mofosyne, Jul 21 2014

I like the idea [+]... But I assume to make this useful the thief either has to not know about these devices (unlikely) or not be able to find the device. As a sticker-type RFID, it seems this might be hard to hide in some cases, but these could come in other form factor to help with that.

The design would have to be really careful to ensure that there are no EM emissions from the processor in the RFID while checking for code or else it might be possible to create a device to detect the presence of the challenge response RFID.

This reminds me of the radar detectors, radar detector detectors (for states where detectors were illegal), and stealth radar detectors that would shut down to avoid detection when they detected a detector detector.

Unfortunately this is likely to be somewhat of an arms race, so you'll need to upgrade your RFID tags fairly often to avoid easy detection.

I thought about maybe having such an RFID manufactured into the device, so then everyone knows it's there, but you can't remove it without damaging the protected item. In that case, you could pretty much go with a standard RFID (foil covered for privacy) or just the printed serial number.
-- scad mientist, Jul 21 2014



random, halfbakery