A microcomputer (23) contains a marking memory (232) storing a transmit sequence consisting of the transmit marking and N consecutive transmit signals (SI). The sync unit synchronises the reference generator (233) to the reference marking which is identical to the Nth transmit marking in the transmit sequence when within the sync. region a reference sequence comprising N reference markings is present which is identical with the transmit sequence. The sync unit synchronisies the reference generator in the absence of synchronisation to a reference marking identical with the received transmit marking when this transmit marking within a trapped sequence of reference markings is present that extends only over a part of the sync. region at its beginning. 
ELEKTRONISCHE SCHLIESSANLAGE MIT MINDESTENS EINEM SCHLOSS, INSBESONDERE FUER KRAFTFAHRZEUGE.