I took apart a vintage cast-iron lock the other day. Inside could be found a delightfully American engineering solution. There’s a deadbolt bar that can only be slid once a spring latch has been tripped.
It’s not the most precise locking system in the world (although one of the more rugged I’m sure), so I twisted a bike spoke into a skeleton key.
It totally worked!
Now I will never be locked in a Victorian mansion against my will by a Nancy Drew villain.