Many years ago, when everybody had Nokias with the Bluetooth on, I used to do a similar thing.
I created a S60 python script that kept scanning Bluetooth mac addresses and link them with the cell tower I was connected to (no GPS yet on mobiles).Then later processed the logs to see if I encountered the same people in different locations and times.
And yes, I re-encountered a bunch of Bluetooth mac addresses in different locations. For me it was fascinating at that time :)
Airguard kind of does this: https://github.com/seemoo-lab/AirGuard
It'll scan for bluetooth trackers in the background (and airpods and iphones) and can give you a per-device history.