Many different types of electronically controlled security locks for safes and the like are known in the art. Examples of such "lock boxes" are disclosed, for example, in U.S. Pat. Nos. 4,926,664, 5,020,345, and 5,033,282. The simplest and most practical type of lock box utilizes a dead bolt which is biased into an extended or locking position by a spring and is withdrawn into a retracted or unlocking position by an electromagnetic solenoid. Such locks, however, suffer from certain deficiencies which may permit a person familiar with their construction and manner of functioning to pick or otherwise defeat the lock. For example, such locks may be defeated by applying an external prying force to the dead bolt in a way which overcomes the biasing of the spring. Such locks may also be defeated by applying an external jarring force to the lock by dropping the safe where the lock is incorporated, by exerting a heavy blow in a direction opposite to the movement of the dead bolt, or by jolting the lock in some other manner which overcomes the biasing of the spring.
More complex types of electronically controlled security locks are disclosed in U.S. Pat. Nos. 4,745,784, 4,904,984, and 5,249,831. Such locks include rather complex mechanical or auxiliary latching arrangements disposed within the lock box for retaining the dead bolt in the extended position. Such latching arrangements, however, are not only costly to manufacture, but difficult to assemble and prone to malfunction.