How does a master key system work?
In a normal pin tumbler lock, each stack of pins has one split point, so only one key cut lines them up. In a master keyed lock, some stacks get an extra thin pin called a master pin. That adds a second split point, so two different keys can turn the same cylinder: the person's own key and the master.
Keys are set up in levels:
| Key level | What it opens | Who usually carries it |
|---|---|---|
| Grand master | Every lock in the system | Owner or building manager |
| Master | One group of locks, like one floor, one department or all the suites in a building | Floor manager, superintendent, cleaning lead |
| Change key | One door (sometimes a pair, like a suite deadbolt and lever) | Tenant, employee or unit owner |
Big campuses can add another level above the grand master, but most offices and small to mid-size buildings only need two or three levels.
How do you plan a master key system for a building?
The planning matters more than the hardware. We start with a list of every door and who needs to open it, then build the key chart from that.
- List every door and lock you want included, even padlocks, gates and cabinet locks.
- Group the doors by who needs them: by floor, department, tenant or trade.
- Decide how many levels you need and who gets each key.
- Pick the keyway and cylinder type. Standard keyways cost less. Restricted ones stop unauthorized copies.
- We work out the key chart, pin every cylinder, then cut and stamp each key.
- You get the keys and a record of which key opens what.
Plan for growth. If you might add a floor, a unit or another tenant space later, say so now so the chart leaves room. Adding doors is much easier when the system was designed for it.
Need master key systems now? A real person answers 24/7.
Call (647) 367-8113Should master keys use a restricted keyway?
In most buildings, yes. A master on a standard keyway can be copied at any key kiosk in a couple of minutes. If one walks out the door, every lock under it is exposed.
Restricted keyways from brands like Medeco, Mul-T-Lock, ASSA and Abloy use controlled key blanks, so copies only come from an authorized source with your signed approval. Our high-security keys page explains how that works.
A 'Do Not Duplicate' stamp on a regular key doesn't stop copying. Plenty of kiosks cut them anyway. A restricted keyway is the only real control.
What should I do if a master key is lost?
Assume someone now has access to every door that key opens. The fix is to rekey every cylinder under that master and cut new keys.
- Change key lost: rekey that one door. Everyone else's keys still work.
- Master lost: rekey every lock in that group and cut new masters for whoever holds them.
- Grand master lost: rekey the whole system.
That's why masters should go to as few people as possible, signed out in a log. Rekeying keeps your existing locks and only changes the pins. Our guide on rekeying vs replacing locks covers when new hardware makes more sense.
Are master keyed locks less secure than regular locks?
A little, and it's worth knowing why. Extra master pins mean more ways for a key to line up, which makes picking slightly easier. With poor planning, a key from inside the system can sometimes turn a lock it wasn't meant to.
Good planning keeps that risk small. Use only the levels you need. Keep sensitive rooms like the cash office, server room or pharmacy stock room off the general master, or give them a high-security cylinder on their own key.
What happens when you call?
Send us your door list
Tell us roughly how many doors, which lock brands you have, and who needs access to what. A rough list is fine to start.
Plan the levels together
We go over who gets a grand master, who gets a master and what stays off the system.
Price before work
You get the price for cylinders, pinning and keys before we start.
Pin, install and test
Every cylinder is pinned and tested with its change key, its master and the grand master before you sign off.
Page reviewed October 2026 by the LocksmithGT team.