Train (and other sets) that run on Bluetooth

[JohnsLegos]

I have been wondering this since I bought the large large Lego Cat bulldozer and most recently my City Train set. I noticed that both of these sets use Bluetooth to control them and was wondering that if I was running either of these sets (using a phone with the apps on them) is that if someone else can "tap into" the controls and run it also?? Is this possible or once it is "locked in" to one set of controls it cannot be over-ridden. Just curious......

[Lok24]

Each hub in the sets can only be conencted to one smart device at a time.