Abstract: A locking device including both a mechanical lock operable with a key and an electrical lock, operable from the same key. The device includes an electrical circuit for operating the electrical lock. The electrical circuit has a microprocessor and memory which stores the identity of keys authorized to open both the mechanical lock and electrical lock. A master key is provided which includes at one end a connector which engages a connector within the mechanical lock when inserted. Information is read from the master key, identifying a set of keys which are authorized to open the lock. Whenever a key from the set of authorized keys is inserted in the lock, an identification number is read through a contact member from a memory associated with the key, and an electrical signal is generated by the electric circuit of the lock to operate the electrical lock.