RFID
Controversial RFID technology identifies products according to a radio frequency signature. It is so small and cheap it may even be embedded into currency.
There are potential benefits to consumers; but potential risks to privacy.
See w:RFID
http://www.thoughtcrimenews.com/rfid.htm
Money plans: http://news.zdnet.co.uk/hardware/chips/0,39020354,2090580,00.htm