cover story: "Tag It!" - electronic design magazine 5-12-05

RFID, or radio-frequency identification, is a short-range wireless technology. It goes beyond bar coding to mark, identify, and track everything from products to people.
RFID uses electronic tags or smart labels to electronically store a unique identifying number instead of a printed bar code. Each tag consists of a single chip with an EEPROM containing the ID number and a radio transceiver or transponder. A popular tag format is a chip mounted on a plastic sheet that contains an antenna in the form of a small loop.

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The other major piece of the RFID system is the reader. Also called an interrogator, this high-power transceiver....uses a larger antenna to interrogate the tag. Passive tags receive the RF signal from the reader. Then rectify and filter the signal into a DC that powers up the transponder circuits, which in turn transmit the tag's ID code back to the reader.

-----as these generation of readers goes, they can only read up to 20ft. but they speculate that the new Gen 2 technology can go much further. Possibly the technology the gov't will use in their national ID cards. You won't even know that its being read or tracked.
--wtbymark