In order to protect a device (20), a transmission device (4) transfers a signal to the device, as soon as a closing cylinder (2) is actuated with a key (1) and a stationary housing (10) is unlocked or locked, which is configured for physically protecting the device against unauthorised access. This is very well suited for application in an industrial setting and is significantly easier than methods known in the IT-world for user authentication and authentication checking. There is the risk that access codes are known to a large group of people and that identical access codes are configured for a plurality of components. A provided mechanical closing system can be very easily retrofitted, in that the transmission device, for example, is arranged in such a way that it is actuated by the closing cylinder, or in that a closing cylinder is used which comprises the transmission device. Authorisation information or role information can be electronically stored on the key, which is evaluated by a hardware security module (5). In this way, a multiple user authentication is prevented.