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I don't even think it's technically possible. Unless a bluetooth device is in discoverable mode it shouldn't be possible to identify them.

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I interviewed at a place that managed traffic light behavior and they had a system to evaluate traffic efficiency by watching traffic flow through the whole area, tracked using ambient Bluetooth signals from phones.

>tracked using ambient Bluetooth signals from phones.

What does this mean? Are they just measuring radio power levels in the 2.4GHz spectrum, and using that to determine whether a car is there or not? Or are they actually somehow capturing bluetooth signals, decoding them, and extracting identifiers (eg. MAC) from them?

It was explained to me as if they track individual cars so I assumed they extract identifiers. I don't know much about BT so I had no reason to question if that was possible. I asked about TPMS as an alternative and they said bluetooth was more reliable since many cars didn't use in-wheel transponders.

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