Abstract: In a system for the transmission of data between at least one write/read station and a plurality of data Carriers, inductive coupling is used to transmit energy and clock pulses from the write/read station to the data carrier. Data is transmitted either in the opposite direction only or bidirectionally. The data carrier in accordance with the invention is provided with a random number generator (6) which can store a random number in a memory (3), preferably under the control of the write/read station. If this random number forms part of the code to be transmitted by the data carrier, a so-called rolling code access control system can be simply implemented, that is to say an access control system in which the codes are changed at regular intervals.