Abstract: A data interface assembly for the transfer of data between a processor unit and a smart card is disclosed which includes a receptacle 20 for receiving a smart card 10, the receptacle having electrical communication means 25 for establishing electrical communication with electrical communication means 12 on said smart card; and a solenoid 22, 26 for locking the smart card in the receptacle upon establishment of electrical communication between the respective electrical communication means. Data transfer enabling means operates in response to operation of the solenoid to allow data transfer for modifying data stored in the smart-card and/or the processor unit when the smart card is locked in the receptacle by the solenoid and to prevent such data transfer when the smart card is not locked in the receptacle by the locking means. The data transfer enabling means is activated by a photoelectric cell 24 which senses the condition of the solenoid.