quick before the internet cops find it: LINK
WondersHowTo has an article on RFID chips, and how to detect and/or block RFID signals.
RFID chips are everywhere. They're in passports, credit cards, and tons of items you've bought in the last 5 years or so. Big retailers like Walmart started using tracking products with RFID as early as 2004, and today, they're used in everything from mobile payments to hospital record systems. Chances are, unless you're a hermit (in which case you wouldn't be reading this anyway), there's an RFID tag within a few feet of you.
and the good news?
Blocking RFID SignalsYou can block signals from being transmitted to and from RFID chips with metal, and almost any kind will work. You could just wrap all your stuff in aluminum foil, but if you want to be a little more stylish about it you can buywallets with RFID protection or even make your own.
so apparently Signs was right: TinFoil hats do work