http://www.activistpost.com/2010/07/...ed-traced.html
Example:
RFID -- Forget your credit cards which are meticulously tracked, or the membership cards for things so insignificant as movie rentals which require your SSN. Everyone has Costco, CVS, grocery-chain cards, and a wallet or purse full of many more. RFID "proximity cards" take tracking to a new level in uses ranging from loyalty cards, student ID, physical access, and computer network access. Latest developments include an RFID powder developed by Hitachi, for which the multitude of uses are endless -- perhaps including tracking hard currency so we can't even keep cash undetected. (Also see microchips below).
More at the link above.