How to listen quietly for other Bluetooth devices?

[Maksim Yevmenkin]

> Doesn't "inquiry" imply activity?

yes, device will go into "inquiry scan"

> I'd like the computer to listen passively...
> I assume, if a phone nearby is communicating with something (like headphones),
> other Bluetooth devices hear it - even if they typically ignore it. Is that a valid assumption?

well, yes and no. bluetooth is basically TDMA (time division multiple
access). what it means is that each device is assigned time slot in
which it can communicate. so, device will effectively "not
listen/talk" unless its in the assigned time slot. i'm simplifying
things a lot here, but, i hope you get the general idea

> Can a Bluetooth dongle be placed into some sort of "promiscuous" mode instead?

not that i know of. bluetooth scanners exist (as completely separate
units), but they are (or at least used to be) expensive. those are
used to grab over-the-air transmissions and decode them. i'm not aware
(not have i ever seen) of-the-shelf bluetooth dongle that is capable
of going into "promiscuous" mode.

thanks!
max