Abstract: An electronic device that can be mounted onto almost any type of key, for indicating the lock/unlocked status of the lock operable by the key. The electronic device includes a processing unit that when rotational torque force being applied on the key, the processing unit identifies depressed contact sensors, and determines whether the lock was last rotated clockwise (typically locking direction) or counterclockwise (typically unlocking direction). Data representing the rotation direction is stored in the memory. When a designated switch is operated, the electronic device activates an indication that indicates whether the lock is in a lock state or in an unlocked state, according to the data stored in the memory.