My cousin has an external door with a knob lock and a double-deadbolt lock. She prefers not to keep the deadbolt locked. If she goes out through that door, she normally turns the knob, leaving the lock engaged, exits, and pulls the door closed, expecting it to lock as it closes.
The problem is that it is possible to close the door such that it feels fully-closed, but isn't quite closed enough to allow the lock to spring into place, and unless she's taking particular notice, it's not obvious to her that the lock hasn't closed. Then, the door remains unlocked, and a strong enough wind later in the day can cause the door to blow open.
The most obvious solution to this problem is simply to be more vigilant about making sure the door is fully closed and locked every time. However, I am wondering if there's some physical modification that she could make to the door that would make it less likely that a momentary lapse in vigilance would result in the door being non-obviously unlocked.
What modifications could be made to this door either to make it so that it's obvious to even an absent-minded user when it's fully closed and locked and when it isn't, or to ensure that it closes fully every time?
If this can be done with a minor adjustment or modification, that would be greatly preferable to any major equipment or structural changes.
Here are photos of the strikeplate, the metal box behind it, and the cavity in the wood behind that. Note the indentation in the wood where the upper-right edge of the strikeplate fits snugly. Note also that there isn't room in the cavity for the base of the metal box to move to the right.
