Thinking about it further, here's an easy protocol, if you happen to have a push-button ignition vehicle: Toss the key fob into the back seat as soon as you get

Thinking about it further, here's an easy protocol, if you happen to have a push-button ignition vehicle: Toss the key fob into the back seat as soon as you get in. The car will still start. Now, when you leave the car, you have to go retrieve the fob before you can lock it. So this forces you to look in the back as part of your car locking habit.