The user has a credit card incorporating electronic devices and/or circuits. The facility which is to be protected has an electronic device and/or circuit analogous to that of the credit card. The devices of the credit card and of the facility contain in their respective memories a secret code S, an...http://www.google.de/patents/US4471216?utm_source=gb-gplus-sharePatent US4471216 - System and process for identification of persons requesting access to particular facilities
