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Sub-master keys

Locks and keys have been used for centuries to safeguard valuable assets and property against unauthorised access and they continue to be used for the same purpose.

From the oldest lock and key device found in the ruins of Nineveh to the modern keyless smart locks that we have today, we surely have come a long way.

A master key system is a popular keying system used in various residential, commercial, and industrial properties that allows for easy access control and management.

It is made up of several levels of keys and provides property owners and managers great convenience by reducing the number of keys to be managed.

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


Before we talk about sub-master keys and the various other levels of a master key system, you need to understand what a master key system is and how it works.

A master key system is a set of locks that are keyed in a way that they each have their individual key and are also opened by an additional key called a master key.

Master keys have become fairly common among property owners as they significantly increase control and improve security by limiting access and reducing the number of keys to be managed.

Under this keying system, you can use a single key to open different locks within a building. It is highly customisable and can be changed and adjusted according to your requirements.

They are ideal for all types of buildings, especially ones that have several access points and can benefit from the added security of the system, such as offices, banks, factories, medical facilities, educational institutions, and multi-tenant buildings.


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 which is clearly depicted in your 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.


A sub-master key also referred to as a change key, is the lowest-level key in a master key system. It will open only one lock and locks that are exactly the same.

Locks opened by sub-master keys can also be opened with the use of master keys and the key levels above that rank.

These keys are carried by individuals who need access to a specific lock or location and not full key access, such as employees, staff members, and tenants.

In order for a system to be considered a master key system, it needs to have at least one level of master keys above the sub-master level.

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

Sub-master keys

Sub-master keys, also called change keys or user keys, are another name for the regular keys that allow you to open a single lock, like the front door or your office door.

They are given to individuals who do not need high-level access since they are at the lowest level of master key access and cannot open any other doors.

Master keys (MK)

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.

They can open all access levels beneath it and are usually designated to individuals who require a high level of access within their area.

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 (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.

They are generally used in places that require a more granular approach to security and are more commonly used in properties such as school systems and districts, hospitals, universities, offices, hotels, and residential flats.

Great grand master key (GGMK)

The great grand master key (GGMK) is the highest-level access for a master key system that can open all the access levels beneath it. It allows access to the entire organisation, including all the doors, locations, and facilities.

They should be given to only certain people within the organisation who require complete access as it will limit the number of individuals with high-level access and make your master key system as secure as can be.


When used in a master key system, sub-master keys and their senior keys can offer several benefits in terms of better security, management, and control.

The benefits of using a master key system include:


Different keys for every door on a property can be quite confusing and stressful for the people in charge of them. Not only are they inconvenient but can also present security threats as they are prone to getting lost, stolen, and misplaced.

A master key system allows you to access all or some areas of a property with one key only. This makes things very convenient, especially in times of an emergency such as a fire in the building. You wouldn’t have to waste time rummaging through a bunch of keys looking for the right one.

Increased security

A master key system allows you to design your key distribution hierarchy in such a way as to give employees, tenants, and other occupants access to only the areas that they need access to.

In a business setting, it gives different employees different levels of access and authorisation depending on their roles within the business. For instance, a CEO would have a higher level of access control, i.e., access to more areas of the business, than an employee.

Also, one key opening several locks means fewer keys being distributed among the employees which would subsequently mean fewer instances of the keys getting lost or stolen.

Higher level of control

A master key system makes duplication of keys very difficult, giving property owners more control over the keys and the individuals in possession of said keys. There are also restricted master key systems that have a registered design, meaning that only a specific locksmith can duplicate the keys, that too after permission and verification.

Additionally, the system allows you to keep track of the number of keys and the people who have them. In case of an intrusion or theft, you can easily track down the people who have access to the area in question and take the necessary action.


While master key systems offer great advantages in terms of better security, management, and control, there are a few drawbacks that you need to make yourself aware of.

The biggest weakness of a master key system lies in key control. Since master keys can unlock not one but several locks within a property, if an unauthorised individual gets their hands on, say the grand master key, every lock in the system may have to be rekeyed or replaced.

The way a master key system is created determines the level of access each individual will have in the system. Therefore, it is best to have a clear idea about your security requirements and access permissions before you implement them in your organisation.


To create a master key system that includes the sub-master keys, master keys, grand master keys, great grand master keys, and so on, you need to consider a few important factors to ensure all the vulnerabilities, if any, are covered, and the system is fool-proof in terms of security.

The first step includes identifying all the doors that are going to be a part of the keying system, followed by creating a hierarchy that matches the hierarchy of the users and/or structure of the building.

For example, a building may have five floors, each for a different department, in which case, you may assign sub-master keys for each room and master keys for each floor.

These keys can be created differently for different users. For instance, a maintenance worker may have keys that access only the utility and machine closets and the building entrance.

Access permission policies need to be properly laid out to outline who will require access through the various access points within the organisation.

Along with the access permissions, it is also necessary to assign access restrictions to the users since they determine the type of users that won’t be permitted to access high-security areas.

Key tracking is another important aspect of key management that allows the property owners to keep a record of all the access permissions along with the people responsible for them.

All keys must be stamped with unique serial numbers and assigned to a particular access level. This record-keeping allows you to keep track of who the keys are given to, who approved the access permissions, and the dates of issuance and return.

Lastly, you need to properly store the keys to make sure they stay out of reach of unauthorised individuals.

There are different types of storage cabinets depending on the number of keys included in the system, all of which make it possible to locate the keys, identify if any are missing, and track who is responsible for each one.

Many property owners are now turning to electronic key management systems, which are cabinets made of steel and require a code or proximity access card to unlock them.

In addition to providing safe key storage, they also keep a digital record of key issuances and users and send automatic notifications when the keys are not returned on time.


Many property owners are moving away from the traditional lock and key systems and upgrading to electronic access control systems, also called keyless door entry systems, in order to eliminate the need for physical keys and for better access management.

There are several types of access control systems, from simple ones that use intercoms and electronic locks, to more technologically advanced biometric systems.

Instead of using a conventional metal key, keyless entry systems work using different types of electronic access control methods that communicate with the electronic locks via proximity sensors.

With these systems, when someone wishes to unlock a door, instead of finding their keys and fumbling with the lock, all they have to do is present the correct credentials to the reader.

The most common types of keyless entry systems include proximity key cards, key fobs, mobile access control, biometrics, or a combination of these.

Choosing the best keyless entry system depends on the size of your property, the budget you have for security, and the capabilities of the system.

If you are upgrading from traditional locks, a professional access control installer will have to wire the premises for the system and set up the electronic locks.

However, if your property already uses electronic door locks, the system can easily be upgraded to one most suited to your needs.


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!

Photo by Chunli Ju on Unsplash


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