I've hit the button to shut off the car and come back to it hours later with the engine running. You really need to press it fully and then watch the tach drop to zero because it idles so quietly
If I leave my car running, and get out with the fob in my pocket, it starts to beep at me, quite loudly I might add.
There's no way you can exit the car with it running and not get some kind of warning.