I’ve been puzzling over this since yesterday. At work, we have a safe. In the safe is a drop box that we put the money we’re going to deposit. A few times a week, an armored car comes to pick this up. You open the drop box with two keys.
To me, the simplest way it would work is to have two separate latches, but this isn’t the case. It appears that one latch is operated by both locks. Unfortunately I can’t really study it and see exactly how it works because I don’t want to keep the armored car guy waiting, so I’m turning to you guys. Does anyone know for sure how they operate?
From what you describe, I’m assuming that (since these are physical key locks with one apparent locking mechanism needing to be actuated by multiple keys) this is to provide “level 2” protection against an inside job. If you need both keys to be turned more or less in tandem, and the key sites are more than a fathom apart, no individual (without some ingenuity) can unlock the safe.
It’s basically a way of tightening security. If you’ve got one bad “cash pickup guy,” you run a high likelihood of him saying that he got robbed or something. If there are always two people required to open a vault, then inside theft requires conspiracy. That means (a)greater jail terms and, therefore, less likelihood that someone would try it, and (b) greater difficulty in pulling the job off (what if bad guy #1 tried to recruit bad guy #2, but bad guy #2 was trustworthy?).
Dual control is what you’re seeing, and is the same principle applied to safe deposit locks. The bank holds the “control” or “guard” key, you hold the “renter” key. Without both, the lock will not open. Assuming that it is an ordinary safe deposit lock (ex: S&G 4440), the lock has two sets of wafers which must be placed into alignment by their respective keys before the bolt will retract into the lock case.
I quite frankly don’t know for sure. Howeve I do notice that when I go to my safe deposit box the bank employee always turns the bank key first and then my key. I suspect that the bank key pulls a detent in the opening mechanism and my key actually opens the door.