Also I can’t see how unlocking the doors would command the glow plugs on. Surely you’d just end up with a flat battery especially if you were a seriel door unlocker/locker? I’ve got a common rail VAG product to look at tomorrow so I’ll check your theory/information.
Unlocking (or opening) a door does loads of stuff on a modern car. Fuel pumps fire up, computers wake up, the sat nav starts acquiring satellites, the headlights run a self test…
I’d bet that most people who go to a car and unlock it after it’s been sat for a while have some intention of driving it. Because it’s a car. 30 seconds of glow plugs won’t drain the battery.
You can tell in cold weather because you can hear relays clicking as high power consumers connect to the battery, and partly because if you spend ages fannying around getting stuff out of the car and then go to start it, you have to wait for a glow plug cycle before the computer will turn the engine over.