I always wonder about the key duplication.
If you make a duplicate where I'm from, due to keys being serialised and registered, the owner would be informed alongside the housing and management companies, if it is a flat house. Not to mention, if the door uses certain locks, they wouldn't even make a copy without proof of ownership.
But I guess that's just us being sensible about security.
You are assuming that locksmiths are uncorruptable. I am pretty sure there's ways to convince them to make one off the books, just as a little favor, but don't tell anyone.
Oooor you can buy some keyblanks and metal files and go make your own duplicate.
Some companies do tightly control access to the blanks, so duplicating their keys does become more complicated. But it isn't like you don't have a copy of the keyway on the existing key, it just becomes a more complex process.
And if all else fails... make a mold of the key and go melt some metal. This also means you need access to it for less time, because making a mold is a fairly fast process and can be done independent of the other steps.
There are many ways for a determined assailant, stalker, or weirdo creepazoid to duplicate a key without triggering any manual safety mechanisms. Even if a key expressly says "DUPLICATION PROHIBITED" right there on the key head.