This is a picture of our car keys. The buttons on them piss me off more than they perhaps should.
So, the keys have two buttons... a big one that can be used to lock and unlock the car, and a second, smaller one which, when the car has first been locked by the main lock button, will double lock the car.
This is not the only car that has this two lock feature on the key fob, the two Fords we had previously did as well.
Locking a car is a binary operation, you either want it locked or unlocked. During my entire history of owning and driving a car, I have never once wanted to *slightly* lock my car. So why have two buttons and two lock states?