Master Key Systems (Most of this applies to both residential and commercial.)

A “master key system” can be as simple as two keys fitting the same lock or as extensive as a school or hospital with tiers and layers of master, sub-master, grand, and grand-grand master keys where a dozen keys might fit the same lock.  That said, a Master Key System is not limited to larger facilities and the concepts can be applied to single households as easily as large corporate entities spanning several countries.

Master key systems can be very, very complicated and both the cuts on the key and the shape of the key itself can be used to create exclusive and permissive keys and keyways.  In these systems, when using physically cut keys (such as most homes and businesses have) all it takes is the loss of one master key at a given level to require the rekey of all the keys and keyways below it.

There are many options to reduce the risk of a lost or duplicated key that compromises this system such as using a particular manufacturer’s exclusive key blank that cannot be copied by another locksmith or incorporating a combination of technologies such as both physical and electronic.

The benefits of these considerations can easily apply to single households that require both family and servant accesses to various portions of the property.  For example, while the parents might require access to all locks on the property, they may want their younger children only to access a side door when they return from school - the cleaning staff only to access the kitchen door and certain closets - the gardner to access the garage and gate padlocks - and still have a key in reserve that can be left for the cable repair man that only works once on the front door but then fails on a second attempt.