Abstract: A device with a key-operated lock cylinder acts on a switching device as a function of the turning of a key. In addition to the key channel for holding the associated key and the tumblers, the cylinder core has a permanent magnet on its periphery. Similarly, in addition to a locking channel for the tumblers, the cylinder housing has at least one sensor which, when the cylinder core is actuated by the key, responds to the permanent magnet and activates the switching device via an evaluator. In order to secure the device against theft as a result of an unauthorized person replacing the cylinder core in the lock cylinder, an entire group of different cylinder cores is associated with the cylinder housing. They differ from one another with respect to at least one of their permanent magnets. In the device a given pair of cylinder core and cylinder housing is used as the lock cylinder which then has a given magnet code.