A master key system is a table of numbers. Every cylinder's pin stacks are specified to a thousandth of an inch and the schedule records exactly how many keys of each level were cut and to whom. Eleven cylinders in this school have been repinned to a combination that is not in the table.
I am a locksmith and I hold the master key suites for a number of schools and a hospital.
How a suite works, because it is simpler and stranger than people think.
A pin tumbler cylinder has five or six stacks of pins. The height of each stack decides the depth the key has to be cut to at that position. A master keyed cylinder has an extra pin in some of the stacks, called a master wafer, which creates a second height that also works. So two different keys open the same lock, and neither is a copy of the other.
To build a suite you choose the combinations on paper first. You write a table: the grand master, the sub masters for each floor or department, and every individual key, and you choose them so that no accidental combination opens anything it should not.
That table is the suite. Without it you cannot add a door or replace a cylinder without risking cross keying, which is a lock that opens to a key nobody intended.
I hold the table for this school in a safe and a copy in a deposit box, and the school has never had it.
In 2023 I was repinning eleven cylinders in the technology and science corridors because a sub master had been lost.
When you repin you strip the cylinder and you measure what is in it, and you write it down, because the first rule is that you verify the cylinder matches the schedule before you change it.
Eleven of them did not match.
What was in them.
Each of those eleven had an extra master wafer in the second and fourth positions that my schedule does not specify.
The wafers are not improvised. They are proper manufactured wafers in standard increments, nought point zero one five of an inch and nought point zero two five, and they are seated correctly and the springs are the right springs.
I measured every one with a micrometer, laid them out on a bench on a piece of white card, photographed them, and worked out what key shape would open all eleven of those cylinders and nothing else.
It is a coherent key.
That is what I want to get across, because a cross keyed lock happens by accident all the time and it is almost always a mess: a cylinder that opens to the wrong key and to nothing else in the building.
This is a designed level. The combination sits properly inside the suite's progression. It does not open the head's office, it does not open the safe, and it does not open the external doors.
It opens those eleven doors, which are the science prep room, the technology store, two stock cupboards, the kiln room, the lift motor room, and five classrooms that all back onto the same corridor.
Somebody sat down with the same mathematics I use and worked out a level that the rest of the suite cannot see.
What the paperwork says.
The suite was installed in 1991 by a firm that no longer exists, and I took it over in 2006 with the table and the key register.
The register records every key ever cut: level, number, date, who signed for it, and when it came back. Seventy four keys over thirty four years and it is in three different hands including mine.
There is no entry for that level. There is no blank, no crossing out, no gap in a numbering sequence. It is as if it was never part of the suite, and the cylinders say it is.
What I did next.
I told the business manager, in writing, in terms she could act on, because a school with an unaccounted key level has a security problem and possibly a safeguarding one and it is not my job to decide which.
We replaced all eleven cylinders. New cylinders, pinned to the schedule by me, at a bench in their own plant room, with her sitting there for the first three because she wanted to see it done.
The school changed its procedures and the keys live in a cabinet with a log now.
I went back in March for an annual check, which is a thing I now do there for nothing.
Two of the eleven have the wafers back in them.
What I have not been able to do anything with.
A cylinder cannot be repinned in the door. You have to remove it, which needs the cam screw out, which needs the door furniture off on that make, and then you need wafers in two sizes and a follower and a plug holder and about ten minutes at a bench.
Somebody with that kit and that knowledge took two cylinders out, repinned them to a level that is not written down anywhere, and put them back, in a school with a camera on both ends of that corridor and a key cabinet with a log.
There is no entry in the log. There is nothing on the cameras. I have watched the relevant nights myself at the manager's invitation, all of it, at four times speed.
So I have written it up properly and given her a copy, and the eleven are on a register of their own that I check every visit with a tester key.
And I have done one thing for myself, which is that the bench I work at in that school is now in the caretaker's workshop and not in the plant room off the science corridor, because the science corridor plant room is where I laid those wafers out on white card in 2023, and I photographed them before I went for my tea, and in the photograph I took afterwards there are twenty two wafers on the card, and in the one I took before there are twenty.