Type of door key Berlin key The Berlin key (also known as, German, Schließzwangschlüssel, or, in English, forced-locking key) is a key for a type of door lock. It was designed to force people to close and lock their doors, usually a main entrance door or gate leading into a common yard or tenement block. The key was a solution to the problem of access via communal doors of such blocks (Mietskaserne) as early as the 19th century.[1] Mechanism [ edit ] A Berlin key has two key blades, at each end of the key, rather than the usual single blade. The key is used like this: Unlock the door from the outside Push the key through the lock, so that the key protrudes from the inside of the door Open the now unlocked door and enter Close…