This proximity tag comes attached to a keychain and is supplied with a pre-assigned unique code. Sealed, nearly impossible to break by accident, it works just like any other proximity card and being attached to keys, is difficult to misplace.
Proximity Card Technology
Proximity cards (or access cards/fobs) are hybrid technology that incorporate a simple electric circuit (proximity tag and coil) imbedded in a plastic card. No battery is needed and the circuit is not removable without destroying it and the card. When the card is correctly positioned with respect to a reader a high speed RF signal passes between card and reader and unique data is transferred.