Berlin Key
The English description on that page doesn’t make it easy to understand what this key does.”Its name comes from the fact that it has two key blades (the part which activates the bolt) at each end of the key, rather than the usual single blade”How does that lead to the name “Berlin key” or either of the German names? I would guess “Berlin key” comes from the fact that it predominantly is used in Berlin.”After unlocking the lock, the key must be pushed all the way through the lock and retrieved on the other side of the door after it has been closed and locked again”I think the main features are:- the key cannot be removed when the lock is open.- you can remove the key from the other side of the door from which it was inserted.It seems you can lock the door from the side it was unlocked from, and remove the key from that side, too. You only have to push it all the way through if you want the door closed and locked with you and the key on the other side of the door.I also think you can close the lock and remove your key when the door is open.