Abstract: A security system for use in secure areas, buildings, hotels, automobiles and so forth. Each lock mechanism is controlled by a decoding circuit having a changeable binary memory. A basic key has two decodable information fields: a key field and an authorization field. When a key field is sensed by the decoding circuit and found to contain a number equal to the combination previously stored in the decoding circuit memory, the lock mechanism is opened. If the comparison does not find a match, the authorization field number and the combination are then compared. If they are found to be equal, the decoding circuit memory changes itself to the number found in the key field and the lock mechanism opened. In this way, lock combinations may be changed. In addition, the key may contain other information fields, such as various levels of master combinations, key insertion information, and so forth.