Two locks. One key. Neither a latch lock (the sort that you can just close behind you and walk away from without turning a key).
When you leave, you have to lock both of these locks manually, with the key. Some days this annoys me, the little faff of standing outside this door in the rain, holding a bike with one hand and trying to pull the door and lock it twice with the other, but I quickly remember why I set it up this way when I arrive at a communal door somewhere else and find that it’s been left open.
Someone left, gave the door a little tug behind them, relying on the single latch lock, but it didn’t latch. Door left open.
I designed the user experience / interface of our door to deliberately annoy and require thought. To force everyone to turn and check two locks in order to leave rather than trying to add some quick and easy ‘clever’ lock that requires no thought.
A real world version of a double opt-in confirmation button, vs the latch lock that’s equal to a delete button with no confirmation at all.
Oh, and the idea that a well fitted latch lock should always latch, or that people should check the latch and not just walk away… never ever ever going to happen to as high a success rate as forcing every user to manually double confirm.