A friend of mine wrote in about my post about the RFID chips I found sewn into some new clothes I purchased at the Gap:

… as a retail veteran, I wanted to tell you that they are indeed commonly used for theft protection. The Gap is too cheap to do anything else with them. When they check you out at the register, they use a de-magnetizer to keep them from setting off the alarm at the door. In this case, Big Brother is not tracking your tshirt purchases, only your tshirt thefts.

Although, it is interesting to note that if you ever want to steal a tagged item, all you need to do is put it in a bag lined in a few layers of aluminum foil. It evidently sufficiently blocks the chip’s signal.

I had heard the bit about aluminum foil, yet I wonder if the chips are in fact RFID, do they have a unique identifier (however difficult to detect from a distance), or do they emit a generic signal?