Real locks in such systems are rare, sometimes even disallowed. Usually, a lock with a real key is only used to temporarily prevent switching on a machine during maintenance or such.
> The PLC is usually in a control cabinet that can be opened by a control cabinet key:
As far as I can tell, that thing's $50. Why would Joe from shipping have one?
> Usually, a lock with a real key is only used to temporarily prevent switching on a machine during maintenance or such.
Most locks aren't really meant to resist and adversary. They're meant to communicate who is allowed and who is not, and back that up by making violations a little non-trivial.
That's the first search engine hit I've pasted. The cheap ones that work just as well are single-digit prices. And usually there is one in every toolbox on the shop floor.
https://www.knipex.de/schaltschrankschluessel?v=2921
Real locks in such systems are rare, sometimes even disallowed. Usually, a lock with a real key is only used to temporarily prevent switching on a machine during maintenance or such.