I've noticed there is no way to unlock doors, once engine is turned on and you've exited the driver seat. I can be holding the fob in my pocket and touching door handle or pressing the fob will not unlock any of the doors. It's as if the key fob buttons and proximity sensors are disabled once the engine is on.

In older cars that require the key in ignition, I do know that key fob buttons disable when engine is on. For smart key based cars, I assumed that proximity sensor alleviates the need for me to go back into the driver door to unlock trunk, other doors etc.