A seat belt buckle (1) and a belt tongue (2) which can be inserted into the seat belt buckle (1). An RFID responder (3) is arranged in or on the belt tongue (2) and an RFID reading unit (4) is arranged in the seat belt buckle (1) and is designed in such a way that a coupling between the RFID reading unit (4) and the RFID transponder (3) is only possible if the belt tongue (2) is inserted into the seat belt buckle (1).