Ford's system - whether you start it with the fob or the app - will lock the doors (well, with the fob, you push the lock button and then start button twice) and start the engine. Once you get to the vehicle, you can unlock it either with the fob or app and it stays running. It won't let you take it out of gear, though. You have to push the start button with the fob in the car for it to fully "turn on".The Mercedes Me app for my GLC63 lets me lock and unlock, and remote start it, but even if I have the fob with me, once I open the doors, the engine shuts off and I need to restart it. If I don't have the fob with me, I cannot open the door with the engine running. I'd have to turn it off with the phone if I want to open the door with the phone. Either way, without the fob, I cannot move the car. Remote app start is strictly for cooling or heating the car prior to getting in.