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Master keys (MK)

Master keys are a fascinating concept that many people often don’t fully understand. How can one key open two doors? Also, how is another key that is opening one of the doors not opening the other?

To fully understand what master keys are, you need to understand how locks work, how a basic lock is converted into a master key lock, along with how these systems are created.

Read on to find out all about master keys, what they are, how they are used, their advantages and disadvantages, and much more:


Many property owners and managers, such as those managing large offices and building complexes, do not want their employees and other occupants to carry around a huge set of keys. Neither do they want to carry it themselves due to the inconvenience they cause.

Additionally, they want to restrict access based on an individual’s position in the organisation, with employees and staff members being allowed to access only certain areas of the building.

A master key refers to a key that allows you to open several different locks that are related in some way in a master key system.

Master key systems refer to a key plan that enables certain keys to open a pre-defined number of doors. They help maintain better security and control and provide quick access to any part of the property when needed, which can be particularly useful during emergencies.


At the most basic level, you need to know that a master key system allows you to open two or more locks using the same key, and to make this work, pin tumbler locks are often used.

Pin tumbler locks consist of a driver pin and a key pin, both of which are lifted so that they rest on the opposite side of the shear line when the right key is inserted. A key must have the right set of grooves in it to lift the key pins to the required height.

If you wish to convert a standard pin tumbler to accommodate a master key system, you will need to add a master wafer in between the driver pin and key pin.

Master keys are related to one another in a hierarchy and letters and numbers are assigned to them and the lock cylinders as depicted in the master key system schematic.

A master key system schematic refers to a diagram or blueprint that allows you to visualise the access levels and key security across the property.

Similar to an architect’s drawing of a property, it translates the vision of a master key system to both allow and restrict access within the property and its different areas.

It also allows you to determine how the master key system will be organised, how many master keys are required, and who will be selected as master key holders before the keys are cut.

The keys at the top of the schematic will fit into a large number of locks while the keys at the bottom may fit only in one.

The fewer levels that a master key system has, the more secure it will be. Therefore, careful planning is critical.


The keys in a master key system are divided into different levels based on how many doors they can open. The number of levels may vary depending on the size of the property and the number of users within the system.

In order of least access to most access, the following are four levels in a master key system:

Sub-master keys:
Also referred to as change keys or user keys, they will open one lock or locks that are exactly the same. The locks accessed by these keys will also open with the use of master keys and all keys above that level.

Master key:
Often shortened to MK, this is the necessary key required to change a simple lock into a master keyed lock. Without it, there is only one key for one lock. Depending on the size of the system, this might be the highest-ranking key in the system.

Grand master key:
Often shortened to GMK, a grand master key is used to access multiple master key systems. It will open all the master key systems under it, along with the subsequent sub-master systems under them.

Great grand master key:
Often shortened to GGMK, this key will open all the grand master key systems under it, all the master key systems under them, and all the sub-master keys under them. You can go even higher with great, great grand master keys, great, great, great grand master keys, and so on, until it becomes too complicated to function.


A master key refers to a key that can open several different locks that are related in some way within a master key system.

For example, an office building may have a master key which will open all the office doors. These doors each will also be opened using a key which would open only one particular office door.

The individual office key, however, may also be able to open a cupboard inside. A single key can be made to open several locks if the locks are keyed alike (KA).

There may be a grand master key designed and cut to open all the exterior doors of the building as well as the conference rooms, data rooms, and offices and cupboards inside them.

If the office is part of a business that operates in multiple locations, there may be a great grand master key that can open all the locks in both the buildings.

These systems can be organised according to departmental, functional, and geographical groups to allow easy access, even during emergencies.


The difference between keyed alike and master keys often confuses a lot of people since they both reduce the number of keys on your key ring and offer incredible convenience. They are, however, quite different.

Keyed alike (KA) refers to a set of locks that can all be opened using the same key. All the locks in this set have exactly the same number of pins and locking elements and can only be opened by one key, or a copy of it. Keyed alike locks are clones of each other, therefore can be opened using the same key.

Master keyed (MK), on the other hand, refers to a set of locks that can be opened by their corresponding master key and their own key.

A set of master keyed locks is referred to as a system and locks in this system can be opened by more than one key. Master key systems also have a hierarchical arrangement and often consist of several sub-master keys and master keys under a grand master or great grand master key.


Master key systems are designed to make it easy to provide individuals easy access to parts of a building where they are allowed to go to while restricting access to areas where they have no business going.

They are used both residentially and commercially and, depending on the type of property and the number of users, you can have two or more levels of master keys.

Starting with sub-master keys and going up to master keys, grand master keys, great grand master keys, great, great grand master keys, great, great, great grand master keys, and so on.

Master keys are generally used for properties such as offices, retail stores, shopping centres, warehouses, factories, hotels, restaurants, cafes, schools, medical centres, hospitals, nursing homes, and residential flats.

They are ideal for multi-tenant buildings since managing access for different tenants can be quite difficult and it could be challenging to manage all the keys.

The best solution for this is to implement a master key system that limits access and gives complete control over who has access to what parts of the building.

They are also commonly used for large businesses that need to grant access to various employees in a hierarchical manner.

A master key system grants access to the employees based on their level and designation in the organisation, minimising security breaches. You may also limit access for low-level employees to areas that they do not require access to, such as rooms where confidential data is stored.


There are several reasons why someone would want to install a master key system in their facility. The topmost reason is increased security in terms of controlling and restricting access.

Here are some of the best advantages of using a master key system:

Easy key management

Managing keys can be a pain, especially since they can easily be lost, misplaced, or stolen, which leads to having the locks rekeyed or replaced. Not only can this be a time-consuming process but can also be expensive depending on the number of locks the lost keys had access to.

A master key system eliminates the need for managing and keeping track of a large number of keys by designating different levels of master keys based on access permissions.

It is an ideal solution for residential, commercial, and industrial properties since it simplifies things and helps prevent unauthorised access to your property.

Controlled access

With the right security measures and controls in place, such as the implementation of a master key system, you can have peace of mind knowing that unauthorised access is prevented and only authorised individuals are granted access to areas that they need to access.

A master key system offers a great level of control over all areas of your property so that you can allow and limit access as needed. You also won’t have to worry about key duplication since master keys prevent it from happening.

Affordable solution

Not so long ago, finding the right security solutions meant paying huge sums of money. Nowadays, with advancements in technology and the rise in demand for affordable security solutions, it has become easier to secure your property without writing out big cheques.

Implementing a master key system is one of the best ways to keep your property safe and secure. It is an affordable and easy solution that allows you to control access to your building without having to worry about lost or stolen keys.

It also gives you more flexibility with how you manage access permissions, given that multiple doors can be accessed using the same key.


Master key systems are super convenient since they offer the ability to open a large number of locks using only one key and allow for better access control and management.

However, along with the great advantages, there are also a few drawbacks which may affect you and your property’s security if you do not account for them before installing the system.

The main disadvantage is that, although a master key system reduces the number of keys, there are still keys to manage and there is no security in place for master keys that are lost or stolen.

What this means is that, like regular keys, whoever has the master keys has access to your property, which can cause a huge security and safety threat.

The higher the level of the lost master key, i.e., the grand master or great grand master key, the higher the security risk. Not only can this be unsafe and inconvenient but can also prove to be expensive. While keyless systems have a higher upfront cost, they are much safer since there are no keys to lose.

Another issue with master key systems is that of upgrading access and changing employees’ keys as they move up the designation ladder.

If you want to allow a certain individual access to a specific area on the property which was previously restricted to them, you will have to take the time out to physically swap the keys.


To create and manage a master key system that keeps the disadvantages to a minimum, you need to take a few factors into consideration when planning it.

  • The brand and manufacturer of the locks and keys since they play a huge role in how reliable the locking mechanisms will be.
  • The location of the doors.
  • The number of locks in the system.
  • A well-planned master key system schematic.
  • The level of access for each individual.
  • Determining who controls the distribution and management of the keys
  • The level of the master key system (the higher the level, the less secure it will be).
  • Stamping the keys with unique serial numbers for tracking and record-keeping.
  • Proper key storage that makes it possible to locate the keys, identify if any are missing, and track who is responsible for each one.


Calder Security has been in the security industry since 1976 and we are members of the Master Locksmith Association (MLA).

We provide all kinds of security solutions designed bespoke to your property’s requirements and are experts in both master key systems as well as electronic and keyless access control systems.

Our expert team of SSAIB approved installers can help you assess your security needs and offer the right master key system or access control system including intercom, proximity fob, card swipe, keypad, and biometric systems that work with fingerprints or retina scans.

We are experienced in creating sophisticated access control systems for residential properties, large scale commercial enterprises, as well as smaller businesses.

We offer expert key cutting services from our Lock and Safe Shop in Wakefield where you can get your keys cut while you wait. We can cut virtually any key to a high degree of accuracy without having to send them away to be cut using our state-of-the-art digital equipment and key cutting machinery.

We can also work on a wide range of locking mechanisms, are specialists in wooden, UPVC, and aluminium doors, and are the official suppliers for leading lock brands including Chubb, Yale, Securikey, and Garrison.

Contact us here or call us on 0800 612 9799 to talk to our professional locksmiths right away!

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