Master Key Systems vs Keyed Alike: Which Do You Need?

If your key ring has grown into a jangling handful, or you manage a building where different people need different access, there are two main ways to simplify things: keyed alike and a master key system. They sound similar, but they solve different problems.

This guide explains how each one works, who each suits, what they cost relative to each other, and how to plan a system that will still make sense in five years.

Keyed alike: one key, every lock

When locks are keyed alike, every lock in the set opens with the same key. Your front door, back door, side gate and garage all use one key.

How it works

Each lock's cylinder is pinned to exactly the same combination. Any key cut to that combination opens all of them. It is the same principle as rekeying, applied across several locks at once.

Who it suits

• Households. One key for the house is simpler and means fewer keys to lose.
• Small premises where everyone who has a key should be able to open every door.
• Landlords with a single property, where the tenant needs access to all external doors.

Strengths

• Very simple to use.
• Usually cheap to set up, especially at the same time as rekeying after moving in.
• Fewer keys to carry, copy and lose.

Limitations

• Everyone with a key can open everything. There is no way to give someone access to the front door but not the storeroom.
• If one key is lost, every lock needs rekeying.

Master key systems: different keys, one master

A master key system gives different people different levels of access. Each door has its own key, which opens only that door or a small group of doors. A master key opens all of them.

How it works

Master-keyed cylinders contain extra pins, often called master pins, that allow two or more different keys to operate the same lock. One key is cut to the individual door's combination. The master key is cut to a combination that works across every lock in the system.

Larger systems add more levels:

• Individual keys open one door.
• Sub-master keys open a group of doors, such as one floor or one department.
• Master key opens everything in the system.
• Grand master key opens several systems, for example several buildings.

Who it suits

• Small businesses where the owner needs access to everything, managers need most doors, and casual staff need only the back door.
• Apartment buildings where each resident's key opens their own door and the common areas, and the building manager's key opens everything.
• Landlords and property managers with several units in one building.
• Offices with shared spaces, private offices and storerooms.

Strengths

• Precise control over who can open what.
• The owner or manager carries one key.
• When one staff member leaves, often only their door needs rekeying, not the whole system.

Limitations

• More planning is needed upfront.
• Costs more than keying alike.
• Every extra level of access slightly reduces the number of possible key combinations, so systems should be designed by someone who understands them.
• Master keys must be tightly controlled. If a master key is lost, every lock it opens is at risk.

Side-by-side comparison

Combining both

Many systems combine the two. For example, in an apartment building:

• Each apartment's front door and mailbox are keyed alike, so residents carry one key.
• That key also opens the common entry, through the master key system.
• The building manager's master key opens every apartment and common door.

In a small business, the front and back doors might be keyed alike for all staff, while the office and storeroom are on separate keys under a master held by the owner.

Planning a master key system

A master key system is only as good as its plan. Rushing it is the most common mistake.

Step 1: List every door

Include external doors, internal doors, storerooms, cabinets, gates, mailboxes and plant rooms. Note what each door protects.

Step 2: List every person or role

Think in terms of roles rather than names: owner, manager, staff, cleaner, contractor, tenant.

Step 3: Map who needs what

A simple table works well, with doors along the top and roles down the side, ticking who needs access to each door. This is often called a key schedule.

Step 4: Allow for growth

Plan for doors you might add, more staff, or a second site. Good systems leave room to expand without starting again.

Step 5: Decide on key control

Decide who can authorise new keys, whether keys will be restricted so they cannot be copied freely, and where the key register will be kept.

Step 6: Install and test

Each cylinder is pinned to the plan. Every key is tested in every lock it should open, and in at least some locks it should not.

Step 7: Keep the register up to date

A master key system only works if you know who holds every key. Update the register every time a key is issued or returned.

Restricted keys and master systems

Master key systems work best with restricted keys. A restricted key uses a profile that only an authorised supplier can cut, and only with written permission from the registered holder. Without restriction, anyone with a staff key could have it copied at a kiosk, and your carefully planned system would slowly fall apart.

For businesses and buildings, restricted keys are usually worth the extra cost. See security locksmith.

What happens when a key is lost

In a keyed-alike system, a lost key means every lock in the set should be rekeyed.

In a master key system:

• If an individual key is lost, usually only that door, and any doors keyed alike to it, need rekeying.
• If a sub-master key is lost, the doors in that group need rekeying.
• If the master key is lost, the whole system is compromised. This is why master keys should be held by very few people and never lent out.

Mistakes to avoid

1. Building a master key system without a plan. It works at first and becomes a mess as doors and people are added.
2. Giving out too many master keys. The more copies exist, the less control you have.
3. Using unrestricted keys. Staff keys can be copied without your knowledge.
4. No key register. You cannot manage what you do not record.
5. Choosing a master system for a single home. Keying alike is usually simpler and cheaper.
6. Mixing incompatible locks. Every lock in a master system needs compatible cylinders.

Which should you choose?

Ask yourself one question: does everyone who holds a key need to open every door?

• If yes, choose keyed alike.
• If no, choose a master key system.

For most homes, the answer is yes. For most businesses with staff and most buildings with several residents, the answer is no.

A worked example: a small café

Here is how a simple master key system might look for a Crown Street café with six doors and four roles.

From that table, the locksmith designs the system:

• The owner carries the master key, which opens all six doors.
• The manager carries a sub-master that opens everything except the cash room.
• Kitchen staff carry a key for the back door, dry store and bin room gate.
• The cleaner carries a key for the front door, back door and bin room gate.

When a kitchen staff member leaves without returning their key, only the three doors on the kitchen key need rekeying. The office, cash room and the owner's and manager's keys are unaffected. Over a few years of normal staff turnover, that saves a great deal compared with rekeying the whole café every time.

Keeping a system healthy over time

A master key system is not a one-off job. To keep it working:

• Review the key register every few months. Check that every key is accounted for.
• Collect keys on the last day of anyone's employment or tenancy, not afterwards.
• Record every new key before it is handed over.
• Rekey promptly when a key goes missing. Waiting only increases the risk.
• Use the same locksmith or keep the system documentation, so the next change fits the original plan.

Costs, in relative terms

Keying alike usually adds little to the cost of rekeying, because the work is very similar. A master key system costs more, because each cylinder needs extra pins, the system needs planning, and keys are often restricted. Over time, though, a master system usually saves money for a business with regular staff changes, because rekeying can be limited to a few doors. Our guide to lock rekeying costs explains what affects the price.

The bottom line

Keyed alike gives you one key for every lock and suits most homes. A master key system gives different people different access, with one master key over everything, and suits businesses, buildings and landlords with several units. Whichever you choose, plan it properly, control who holds keys and keep a register.

For help planning a key system, call Surry Hills Locksmith Service on 02 3820 5414, open 7 days, 7:00am to 12:00am, or request a quote. See commercial locksmith for business work.