The big bundle of keys came to an end. With a multi-level key access system, you solve all your problems so far!
The central locking system (Z) consists of several different cylindrical inserts (keys). Individual keys of these different cylindrical cartridges unlock / lock one or more cylindrical cartridges (= central cylindrical cartridge).

When to use the central locking system (Z)?
The main area where the central locking system is applied are residential buildings. This includes facilities for rented and privately owned apartments. Apartment keys unlock / lock the central cylindrical inserts of the main front door of a building, basement door and garage door, but do not unlock / lock other adjacent apartments.

Master Key System (HS)
Whether in business, commerce or at home: every door must have its own key. This would mean that you have to carry a large bundle of keys with you in order to enter any room.