RFID tags
 

Make a Faraday Cage Wallet

You already have your tin foil hat, and you're pretty sure no one can find you on the Google. However, there's one detail you may not have thought of, and that's those pesky RFID chips.


RFID tags identifying who and -- gasp! —- where you are can be found in passports, ATM cards, credit cards and some state-issued ID cards. The same technology will possibly even be used in paper money in the near future.

read full story here
http://howto.wired.com/wiki/Make_a_Faraday_Cage_Wallet

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little note... you might have read this and said ummm ok this is out there
I dont care..
well lets see this video below how fast a hacker can get to your ID

How to hack RFID-enabled Credit Cards for $8 (BBtv)
http://www.youtube.com/watch?v=vmajlKJlT3U