Seeing this thread, I just did a test with my 2016 Nissan Titan XD.
In order to remotely start the truck, I have to first lock the doors with the remote, then press and hold the remote start button for 5 seconds. After this, I then need to unlock the door and push the start button.
I was able to remotely lock and start the truck from upstairs. I was about 100' away when I did this.
I then went downstairs to confirm that the truck was running, and that the doors were all locked.
I then removed the actual key from my key fob, and left the key fob in the garage - about 30' away. I was able to manually unlock the door with the key. When I pushed the start button the truck automatically shut off. I had to go retrieve the key fob from the garage before the truck would start.
I then re-did the test, but this time I placed the key fob 5' in front of the grille of the truck. Same results. As soon as I pushed the start button the engine shut off.
So at least in the case of the Nissan, the key fob has to be in VERY close proximity (i.e. inside the cab) for the engine to start.
