A master key system answers: who opens what?
It is a hierarchy. Each person carries a key that opens only the doors relevant to them, while a master key above it opens everything below. A sales manager opens the sales area but not the finance office; the operations manager opens both.
Done well it removes the key ring and the key cupboard at once. The design is the whole job — the cylinders are just what implements it.
A restricted key system answers: who can get a key cut?
An ordinary key can be duplicated by anyone holding it, at any counter, for the price of a coffee, and you will never know. A restricted key uses a patented profile that only an authorised locksmith can cut, and only on written authority from the people named on the system's signatory list.
Which one does a business need?
Usually both, and usually in that combination: a hierarchy for convenience, on a restricted profile for control. Three worked examples:
- An office with a reception, a server room and a finance office. The hierarchy matters most — most staff should not open two of those three. Restriction matters because the master is the whole building in one piece of metal.
- A strata building with common entrances, a bin room and a plant room. Restriction is the priority: every resident holds a common key and residents change. Hierarchy is secondary and usually simple.
- A multi-site retailer. Both, heavily. Area managers need one key across several stores, and a key lost in one store cannot be allowed to become a key cut for all of them.
The bad day each system is designed for
For a master key system, it is losing the master. Depending on how the system was built that can mean repinning every cylinder it opened — which is the strongest argument for putting the master on a restricted profile from day one, so at least an unauthorised copy cannot be made from it.
For a restricted system, it is discovering the signatory list has not been updated in six years and includes two people who have left. That is a five-minute administrative fix that nobody ever does until it matters.
When to move to access control instead
When staff turnover is high enough that you are rekeying regularly. At that point a credential you can switch off beats a key you have to collect. It is not either-or — most sites end up with electronic control on the busy doors and a keyed hierarchy behind it.
The signal to watch for is simple: if you are rekeying more than once or twice a year because someone left, you have outgrown keys.