DC Metro riders should be familiar with the SmarTrip Card - a "permanent, rechargeable farecard... embedded with a special computer chip that keeps track of the value of the card" used for Metro fares and parking. They're pretty convenient, but their greatest drawback is that they cannot be used for any of the day or weekly passes.
That complaint aside, I stumbled across this site yesterday where someone managed to take apart a card. They're trying to redesign it into a smaller form and haven't been entirely successful, but it was rather interesting to look at.
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