it's a card that you only need to touch on the receiver device and the device can read the card's data. normally it's used at door access system, toll, etc.
can anyone here post me the information, url, etc.
generaly these systems use RF communication between reader and card.
The card contains a coil tuned to a specific frequency (200 KHz range I think).
The reader transmits continuous RF signal which is used to power the card when it is close.
Card then absorbs energy since it is tuned to this same frequency, uses this energy to power it's electronics and then sends back it's ID by varying the coil tuning.
