How Things Work: Master Key Systems

Max Haley
Dec 1, 2025
2 min read

When it comes to managing access across multiple doors, a master key system is one of the most practical and secure solutions available.

At H Harrold & Sons, we’ve designed and built master key systems ranging from small offices to large multi-building hospital and university estates.

Here’s a quick guide to how master key systems work and why they’re used so widely.

Hands use calipers to measure a metal lock part, reading 0.648 on a digital display. Workbench with tools and papers in background.

What is a Master Key System?

A master key system provides structured, physical access control using locks and keys. It’s built around a hierarchy of keys, allowing you to decide exactly who can open which doors.

What are the Different Types?

Keyed Alike – One key opens several locks.

Keyed to Differ – Each lock has its own unique key.
Master Key – Each lock has its own key, but a Master Key opens a group of locks, which can be useful in places where controlled access is needed for many doors.
Sub-Master Key – These are smaller sections within a larger system, where a sub-master key operates a defined group of locks, while higher-level keys (e.g. master or grand master) can open all of them.
Grand Master Key – This type of key adds further levels of access for large sites with multiple departments or buildings, particularly useful for a senior manager to have access while more restricted access is still required elsewhere.

Where Are They Used?

Master key systems are common in:

Housing complexes.
Offices.
Hospitals.
Schools and universities.
Public sector and large organisations.

In fact, many people use them without realising – for example, flats with shared entrances or staff areas in hospitals and offices.

Why Choose a Master Key System?

Fewer keys to manage.
Stronger security and accountability.
Clear control over who can access what.
Easy to expand or adjust as buildings or staffing change.

What are the Security Options?

A master key system controls who can access a door, but buildings often require specialist hardware to manage how a door functions.

Classroom Function Locks – Common in schools and colleges. Staff can secure a room from the corridor while pupils can still escape safely from inside.
Anti-Barricade Systems – Used in mental health, supported living and welfare environments. They allow authorised staff to override the door if someone inside tries to block entry.
Anti-Ligature Hardware – Designed for clinical and high-risk healthcare settings to remove ligature points and improve occupant safety. These features are separate from the keying system but often used alongside it.