Abstract: The device consists of a key having a passive memory zone and a circulating register, the code contained in the passive zone being intended to be transferred to the circulating register when the key is introduced into a lock, so that the said code may be transferred from the circulating register to the lock to be compared there with a reference code contained in the lock. The key comprises a circuit which is provided with a counter which is incremented each time voltage is applied to the key and a system for resetting the counter to zero, when the code is successfully transferred from the key, so that after a number of attempts determined by the counter of unsuccessful transfer attempts, the passive memory zone is destroyed by the output signal emitted by the counter.