A master key operates a set of several locks. Usually, there is nothing different about the key. The differences are in the locks the key will operate. These master-keyed locks are configured to operate with two, or more, different keys: one specific to each lock, which cannot operate any of the others in the set, and the master key, which operates all the locks in the set. Locks that have master keys have a second set of the mechanism used to operate them that is identical to all of the others in the set of locks. For example, master keyed pin tumbler locks often have two shear points at each pin position, one for the change key and one for the master key. A far more secure system has two cylinders in each lock, one for the change key and one for the master key.
Maison key system
A maison key system is one 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, a 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. ==See also==