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Thanks seamus! Having not dealt directly with RFID and only RF or EM tags, I can really only go into detail on those, although I have seen examples of RFID tags placed in the tops of shampoo products. I also understand that some Hewlett-Packard printers were tested with RFID tags at selected Wal-Marts last year, though I have not been able to determine the construction of those tags (beyond being RFID).

In the case of Checkpoint gates, usually one side of the gate acts as a "master" transmitter. When the receiving side of the gate detects a frequency that has been altered by the tag (and falls within the tuned range) an alarm is triggered. The tag's helical antenna is etched from thin aluminum and bonded to a piece of paper. At the end of the antenna in the middle of the tag is a small diode or RC network that causes the tag to emit a radio signal in response to the radio signal it receives. To disarm the tag, a strong RF pulse (much stronger than the gates emit) basically burns out the diode or RC components, nullifying its ability to transmit RF. Between the gates a burned out or corrupted/defective tag does not emit a signal so the gates let it pass without an alarm being triggered.

HTH

kw5kw wrote:How can this be?

These anti-theft scanners work off of RFID not metal detection.

No, not all (I used to be a District Manager for a software retailer that used two types of anti-theft security gates in our stores).

The type with the slim metal strip, as is often seen encased in a plastic receptical and stuck inside a DVD case or other products for example is called a No-Go strip and operates off of electromagnetic technology. They are also found in book stores where just the strip, covered with paper instead of enclosed in a plastic receptical, is placed between the pages of a book. These are metal strips with magnetic particles for degaussing (desensitizing and resensitizing) and are deactivated (or even re-activated) by a magnetic pad, or "brick" that alters the magnetic properties of the strip, thereby deactivating it. That's what makes these deactivation devices so dangerous to credit cards (and software, which is why we switched). Libraries also use this kind of anti-theft stip and security gate combination.

Another type, Checkpoint, are seen as an adhesive sticker and sometimes even printed with a faux UPC code, but is actually a radio frequency transmitter. It's not RFID, but it is indeed an FM radio frequency of 8 Mhz that is picked up by a different type of security gate sensor. If you were to peel the sticker off the product, you would see a metallic foil "coil" that is actually the transmitter and antenna. There is no "data chip" in this anti-theft sticker, either (such as you will find in RFID).

This type of anti-theft device can be deactivated or "de-tuned" by placing another like-sticker over it, bending the sticker in two, severing the antenna, or even placing regular aluminum foil over the sticker. The sensors have to be tuned at installation, and can become "untuned" by placing metal objects (bins, shelves, etc.) too close to the gates. As well, in many of the gates there seems to be a "dead zone" from floor level to about 6-8 inches high that you have to be careful of, or at least aware of. I've had thieves try to place shoplifted items in the bottom of shopping bags and try to "scoot" them along the floor so the tag is in this "dead zone" as they go out the gate to circumvent it, which is why the best theft prevention is alert employees.

Other tags that use this type of technology are the bulky devices that are clamped on to clothes and apparel, but many of these types of tags may or may not contain a radio frequency transmitter, but they often are filled with a permanent dye that will ruin the garment and stain the person's hands that tries to remove the device without using the proper tool.

RFID tags, even though also using radio frequency, actually contain a small microchip that can be programmed to contain data. This data can then be transmitted to a receiver via the radio frequency channel. That is how the system works to track a particular object. Once a product or device is programmed or "serialized", that information can be tracked from that point on through to it's final destination and is what makes it so convenient for inventory tracking purposes. The transmitting antenna on RFID tags is also stronger than the antenna used on Checkpoint-type tags, and is why the RFID tag's data can be picked up from farther away, allowing tracking of inventory stock from within a shipping container or high up on a warehouse shelf for example.

HTH!