A Maison key system is a keying system that permits a lock to be opened with a number of unique, individual keys. Maison key systems are often found in apartment building common areas, such as main entrance or a laundry room where individual residents can use their own apartment key to access these areas. Unlike a master key system, where each individual lock has one individual operating key and one common master key, Maison lock is designed to be operated by every key within the system.
Because of the inherent lack of security in the Maison key system, some jurisdictions prohibit the use of Maison key systems in apartment and condominium complexes. In such locations, access is usually facilitated by either a high-security, key-controlled system or the use of electronic access control systems such as a card reader.