I haven't tried to track phones with bluetooth, it seems like it wouldn't be possible because phones aren't always announcing themsleves. A by product of battery limitations I would guess. The more common use is tracking powered tags for the purpose of asset tracking in say hospitals or similar.

I didn't know the onboard adapter supported monitor mode, that is ligitmately useful knownledge for me. Thanks, it should be simple to build your own sniffer to just plan around with. Carefull if you are in the EU though, not that it is removely possible to catch a silent sniffer.