Abstract: For controlling a central locking installation and/or theft alarm of a motor vehicle a switch lock installation is provided which comprises at least one lock with mechanical tumblers for the mechanical locking and unlocking of a door or a bonnet of the motor vehicle. The tumblers form a first key secret. The key which blocks the tumblers carries an electrically, magnetically or optically readable information carrier for a second, operationally variable key secret. A reading device detects the information of the second key secret in a position in which the mechanical tumblers of the lock are released. If the key is moved in the opening direction of the lock, a control circuit compares the information read by the reading device with an ideal information stored in a memory circuit and controls the central locking installation and/or theft alarm accordingly.