Coming from the United States down to South America, in Peru, Argentina, and Chile, I have run into a number of home door locks that I don't understand how they're intended to work.
If the door is unlocked, you can exit, but the door locks behind you, needing a key to reenter. I suppose this makes sense and you'd just want to make sure you always leave with the key.
You can insert the key into the keyhole and rotate one direction, quarter turn to open the door, or the other direction one rotation and it engages the deadbolt. Problem is, if someone is still inside, you've locked them in, as there's a keyhole but no turn piece on the inside. That means anyone still inside needs a key to leave.
From the outside, if you rotate the key an additional rotation for a total of 2, I believe it pushes the deadbolt further out, and I only have one key to test this, but I'm only able to get to this state from the outside, from the inside, it only allows the single rotation. I believe this to mean that I could potentially be locked inside with the key but I wouldn't be able to exit? Is this correct?
I'm able to understand the first way the lock works, but the second two baffle me. If there's a fire and the lock is in state 2, I'll either need to break the door down or use the key to leave? If the lock is in state 3, even if I have the key, I wouldn't be able to exit unless I slide it under the door to someone and have them open it for me? My overall question is what are the use cases for potentially dangerous lock states?