A lot of people seem to not understand the purpose of this mechanism, or see the necessity for its complexity.
A mechanism like this (sometimes called a daisy chain, slide bar, or multilock) serves three objectives: accessibility, excludability, and accountability.
Accessibility: there are people who require access through this gate. The simplest solution to this is to leave it unlocked.
Excludability: there are people who are not allowed access through this gate. Can no longer leave it unlocked. "But acdgf, a simple combination lock or lock with multiple keys would work just as well. Why employ such a contraption?" Because of the final objective.
Accountability: if a person not allowed through this gate makes it through, we must know who let them in, and properly discipline them. If you have a combination lock, anyone who learns the combination gains access. After they gain access, all that is left is an open lock. It's not apparent how (from whom) he learned the combination. With a multilock system, it is immidiately obvious which lock was opened, and thus who is accountable for the breach.
Systems like this are used in several industries. Where possible, they have been replaced by biometrics, or unique key cards, as those don't have a limit on the number of people with access and can usually log entries. These analog mechanisms are still employed in utility cabinets/rooms/buildings, farms, construction sites, etc. Anywhere where access must be controlled, but having more sophisticated systems (like card readers or a guard) is impractical.
Looking in hindsight, I could have been clearer about accountability. Maybe you'll want to post this as an edit to add clarity?
Anyways, if someone makes or otherwise acquires a copy of a key for one lock, gains access, does whatever nefarious activities, then leaves and replaces the lock, the other comments are correct in asserting there is no more information here than with a single lock with many keys. This, however, is an extremely rare occurrence.
What does happen far more frequently is: someone authorized opens the gate, then leaves and forgets to replace their lock, leaving the gate unlocked. This is when an opportunistic bad actor would gain access. If it was a single lock with a code or with many keys, you could not tell who forgot to replace it. With a slide bar, however, you can immediately see which lock was left out (by negligence) that granted access to a bad actor.
Other comments mensioned just locking a bunch of locks together, without the slide bar contraption. That works and is very common. The advantage of the slide bar is that you can very easily tell when a lock is missing.
Bitmugger on February 12nd, 2025 at 14:16 UTC »
I've seen this pic before, could easily scale to 8 locks. Looks like it go to infinite locks if you wanted but would be unwieldy.
Just_okay_advice on February 12nd, 2025 at 15:03 UTC »
Collect all 6 keys, then you fight the boss. Or wait, is this not a video game
Spartan2470 on February 12nd, 2025 at 15:05 UTC »
Here is a higher-quality and less-cropped version of this image.
Here shows how this works. Thanks to /u/StinkFiggler over here.
Per /u/acdgf over here.
Edit: /u/acdgf just added: