Can the Bluetooth adapter included in the Raspberry Pi models be put into some sort of "promiscuous" mode -- so that it reports to the host all Bluetooth-activity that it "hears", even if it is not itself part of the conversation?
I'm not trying to break encryption, just want to be aware of any BT-radio activity going on in the device's proximity...
Since there is documentation how to capture Bluetooth traffic with wireshark (or tshark) it might be possible.
Check out this article