There are several forms of biometric identification employed in access control: fingerprint, hand geometry, iris, Voice Recognition, and facial recognition. Biometric technology has been promoted for its ability to significantly increase the security level of systems. Proponents claim that the technology eliminates such problems as lost, stolen or loaned ID cards and forgotten PINs.
A reader radiates a 1" to 20" electrical field around itself. Cards use a simple LC circuit. When a card is presented to the reader, the reader's electrical field excites a coil in the card. The coil charges a capacitor and in turn powers an integrated circuit. The integrated circuit outputs the card number to the coil, which transmits it to the reader.