With my car, trying to lock the doors just doesn't work if one is left open — not always the most obvious failure mode, but it's been enough to get me to notice something's wrong.
> With my car, trying to lock the doors just doesn't work if one is left open
for suburban single family residence dwellers with their own garage, they may not always (or ever) lock the doors while the car is parked in their locked garage.
No car I'm aware of requires this. If the ignition is off and the doors are all closed, the car is, for all intents and purposes, asleep. If anything, doors unlocked may be lower power... as that would disable (or, rather, not enable) alarm functionality.
