Hazel literally tells you.
I'll consider it.
I think for me as a player if I come across something like a door with a code I don't know yet. I leave it alone and wait to come back later.
I give people the option to click that door early because my intent is to make you go "Oh, I'll need a code at some point" not have a bunch of people bang their heads against it and then run to the internet.
I don't like the idea of taking away that choice from the players, but if so many people are stuck on it, I may have to.