There are realtime systems for traffic analysis. I know of Addinsight, e.g. https://news.addinsight.com/bluetooths-leap-forward-the-evol...

Possible, but they buy data from the carriers with similar profile possibilities. The DEA operates long standing and pervasive surveillance in “drug corridors” like I-95 from Maine to Miami. They do things like LPR and grabbing passenger pictures.

If Bluetooth is used, it may be a way to get a count of passengers or if the passengers change. I know based on newspaper accounts that they are particularly interested in cars that stop in Philly or Baltimore.

This stuff is frequently used against cops too so they may use the tech in similar ways. If you’re someone worried about getting raided, spotting a large number of new signals at the front door is an early warning potentially.

I remember an art exhibit by an online privacy activist made where it’d ping people’s phones to get a list of “known WiFi networks” and then display them on a screen in a room.

Each person would get a unique fingerprint of named network locations

I believe Houston used bluetooth to measure congestion on 45.