As you can see, mine is set at 2 minutes instead of 15, but the concept is the same. If the front door lock remains unlocked for 2 minutes and the front door contact sensor remains closed for 2 minutes, then lock the front door. Opening and closing the door at any point restarts the 2 minute timer for the contact sensor.
I also have a virtual switch as a precondition, which allows me to pause the auto-lock for times when I want it to stay unlocked.
Hm. Ok, I will give that a try. I confess I’m not entirely clear on when to use preconditions. I guess I was using them incorrectly before. Also, how do I create a virtual switch? That sounds like a handy thing to have.
(Keeping SmartThings limping along since 2013.)
You can create a Virtual Switch in the SmartThings app by clicking Menu, then Labs, then Virtual Switch…