The invention concerns a device for clearing and/or activating an object, in particular a machine, with a codable key, an input device for inputting a code, a coding device for coding the key with the entered code, a reader for reading a code found on the key, an evaluation unit for evaluating this code,...http://www.google.co.uk/patents/US5969633?utm_source=gb-gplus-sharePatent US5969633 - Device for clearing and/or activating an object
