How it works
A normal lock has one set of pins that line up for one key. A master-keyed cylinder has an extra set of small pins stacked in, so two cuts line up: the change key for that door, and the master key above it. Every door gets its own change key, and the master opens all of them. Larger systems add levels: a grand master over several masters, each master over a floor or a building.
Keyed alike is not the same thing
Keyed alike means one key opens every door, for everyone. That suits a family home. A master system is for when different people should open different doors: tenants their own unit, staff their own area, and the owner everything.
How many levels do you need?
Fewer than you think. A fourplex needs one master over four change keys. An office with a few departments may want a master per department and one grand master. Every level added is another key that can be lost and another way for each cylinder to open, so design from who needs to reach what, not from what the system could do.
The security trade-off
Each extra shear line makes a cylinder slightly easier to pick or bump, and a lost master key exposes every door at once. That is why master keys should be few, held by named people, and why the system should be written down. A key chart, listing which key opens which door and who holds which key, turns a lost key into a planned fix instead of a building-wide rekey.
Stopping copies
A "Do Not Duplicate" stamp stops nobody; plenty of places ignore it. What controls copies is a restricted keyway, where key blanks are not sold over the counter, so a copy cannot quietly appear. For a master system where copies matter, that is the right base. Our high-security locks page covers it.
Living with it
- When a tenant or employee leaves, repin their door to a new change key. The master still works; nobody else notices.
- When a master key is lost, repin the system to a new master from the chart. Planned, not panicked.
- Mixed hardware is the usual obstacle at the start. Locks of different brands on different keyways cannot share a master until the odd ones get matching cylinders.
Our master key system service plans, pins and charts systems for landlords, HOAs and small businesses across the Santa Clarita and San Fernando Valleys.
Questions people ask
Can my existing locks be master keyed?
Often, if they share a brand and keyway. Cylinders that cannot join the system are replaced to match. Photos of the locks and the key faces tell us which is which.
What happens when a tenant moves out?
Only their door is repinned to a new change key. The master and every other key keep working.
Is master keying less secure?
Slightly, per cylinder, and a lost master exposes every door. Keeping levels few, masters few and using a restricted keyway manages both.
Who should hold the master key?
As few people as possible, each named on the key chart. The fewer masters exist, the less a single loss costs.