Usually, I unlock the driver door with the handle, with my Fastkey in my pocket.

Once you've done that, only the driver door unlock, none of the passenger nor trunk door unlock. You can't unlock them even if you wife, on the other side of the car, with his own Fastkey try. The only thing to do is to unlock them with the button inside the driver door.

I often have something to put in the back seat so it bother me to have to do that each time.

I read, in the owner manual, that it can be set to open all the door.

I ask my dealer. He said I'm the first to ask for that... He plug my Outlander to the computer, search for 3-4 minutes and found how to set it.

Now I'm a very happy guy :-))

By default, the passenger door and the trunk will both unlock all doors.

Gosok

This is to prevent car-jacking. A carjacker could enter your vehicle from the other side when you unlock the door.