Master Key System Design: preparing for the visit

A new hire at the shop gets handed whatever spare key happens to be in the drawer, and it turns out to open the stockroom, the back office and the safe room all at once. The owner realizes nobody actually decided who should open what.

Worth answering before the call

Roughly how many doors need to be part of the system? Do any existing keys already open more than one door? Do any doors already use keypad or card-based access?

Can key duplication be restricted so copies cannot be cut elsewhere?

Yes. With a restricted or patented keyway, blanks are only available through the manufacturer's authorized record, so a copy is not cut at an ordinary hardware counter without going through that channel. This does not make a key impossible to duplicate, but every legitimate copy passes through a record the owner controls, which a standard keyway cannot offer.

How is accountability maintained when several people hold different levels of keys?

Through the chart and issuance log rather than memory. Each level is tied to named roles or people, each key is marked to reflect its level rather than the door it opens, and any change of hands is recorded with a signed receipt. That record names every authorized holder for a door, though it can only account for a key that was never copied, loaned or picked up by someone outside that list.