Its a clever system, distance has already been confirmed but even when leaving the car an alarm will alert that no key is present which reminds you to switch off the engine (if start/stop has kicked in) and best of all you cannot lock the doors if the key has been left inside.
What I have recently noticed is that the boot won't open when the engine is on, but maybe this is down to the auto locking sequences of the doors but as soon as I switched the engine off the boot would open.
