What Is a Master Key System?

A master key system lets one 'master' key open many locks, while each lock also has its own individual 'change' key that only opens that one door.

Example: a property manager in Carrboro, NC carries one master key that opens every unit. Each tenant has a change key that only opens their own door. The maintenance crew can carry a sub-master that opens common areas plus utility rooms — but not units.

It's done by adding extra 'master pins' inside each lock cylinder. A locksmith designs the system on paper first (a 'keying schedule') so the math works and no keys accidentally cross-open the wrong doors. Done right, it scales from a 4-suite office to a multi-building campus.