In Houston, TX, USA, I noticed antennas placed over individual highway lanes. It turns out they track the Bluetooth signals from cars to determine traffic. They even have a message on their website saying people should be more worried about license plate tracking.
https://www.houstontranstar.org/faq/traffictech.aspx
On the OEM infotainment center in my vehicle, I can't even find a way to turn off Bluetooth.
You know what you cant turn off? TPMS. I mean you can remove them from your car, but those little guys broadcast and with the right equipment you can track cars with them.
Yes. The IDs are unique, fixed, and easy to pick up. You have to broadcast a low-frequency signal first to enable them and they'll emit a signal. There are several projects on GitHub to pick them up, and I've successfully done it.