My second fob pretty much lives in my truck, in the center console which is about 6” above the front antenna that detects it, and it never wakes the bus up.
If the truck senses the fob, there is no “keeps some computers active”. If it is sensed, it automatically wakes up every module on both buses that are fed battery power. You will know for sure when that happens if you’re sitting in the truck while it’s asleep, because you’ll first hear a faint sound out of the speakers that sounds like a needle being put on a record, and the instrument cluster and start button will illuminate.
Any other noises you hear outside of that, without the cluster coming alive, is just the hvac module doing it’s thing with the doors, and the radio (the radio stays active for one hour after the truck is shut down. This is to allow anything plugged into the media hub usb ports to keep charging).