Those Security Device stickers.

Many things I buy have a 1 1/2" x 1 1/2" sticker that is white on one side. The other side has a circuit board-looking thingy of concentric silver squares and a shiny pink square in the middle.

I assume this is some kind of security device, though not a very effective one, since it can be easily peeled off.

In any case, how does it work? Is there a battery in there? It’s not magnetic, as far as I can tell. Do silver squares always make bells and whistles sound?

Sounds like an RF tag to me. The silver squares act like an antenna. Typically these things rely on the incoming radio wave to build up a charge in a capacitor, which then powers the small chip in the middle so that it can transmit a unique code which is programmed into it.

If you’ve ever seen an ez-pass toll booth it’s essentially the same thing. Some of the longer range tags have a built in battery instead of relying on the incoming radio beam for power.

They might be more for inventory control purposes than security. Security tags tend to be harder to remove. Some stores code a product ID into the tags. Then all they have to do is walk around with a portable scanner, and they can very quickly get a full inventory of every item in the store.

A google search on “RFID tags” will probably get you loads of reading material, including a few rants and raves by the paranoid types who think that RF ID tags are another form of big brother trying to spy on you.

Here is an article from How Stuff Works.

There is no battery in the device: it is passive. The device will resonate when excited with a specific frequency radio wave. Not all silver squares will cause the alarm to sound: the resonant frequency depends on the configuration of the coil and the values of the components in the center.

I just saw a story on Walmart and RFID tags this afternoon, as I was unwinding after work. It was either on CNN, Headline news, or CNBC, but darned if I can find a link to a story through them, through Walmart, or through google, so sorry, I can’t provide a cite.

Basically, the story was that today in Arkansas, Walmart met with their top 100 suppliers, and told them that they wanted all products purchased from those suppliers to be RFID tagged by 2005. The reasons cited were for inventory control and (to a lesser extent) shoplifting prevention.

The story continued on about how this would be a boon to some tech companies, although they would have to watch the costs, because Walmart would refuse to have the cost passed on to them/their customers.

When I worked at Circuit City, we used the type of tag you are describing. They are passive and not easily removed. On a slow day we discovered that if you place two of the tags against each other, the alarm fails to go off. Based on how they are deactivated, I imagine that passing a magnet over them would also work to make them useless but I am not sure. As a theft prevention device, they were not too effective, not because of being removed but because thieves almost always removed the products from their boxes. We once had a guy steal 10 hard drives by cutting the bottom of the box open with a razor, removing the drive and placing the box back. No one noticed till I picked one up and thought it didn’t feel right.