Abstract: A card-key device with an embedded microprocessor is able to communicate with a computer-based security system via an optical connection. The optical connection is made by linking a light-emitting diode with a phototransistor through a "light tunnel" created by a mechanical connection. Electromagnetic sensors and grippers are used to assure each side of the connection that a valid connection has been made, as well as to supply power to the card-key on-board microprocessor. The card-key's on-board microprocessor can be used to retrieve an identifying number, to store data for the security system, or to perform other data transformation functions for the security system.