This is why I think someone should market a cheap SIGINT tool that collects BT/BTLE/Wi-Fi data from nearby devices.
I've got this setup running on a Raspberry Pi near my front door and it collects all sorts of useful data, even from people walking by on the sidewalk, 30 feet and two walls away.
At some point, I'd love to explore vehicle emissions more, too.
No prosecutor is going to waste their time trying to convict someone based on metadata. Even video is often insufficient for a conviction.
Uh hello police department?
I have MAC addresses!
M-A-C...
Yes, I sniff them out the air with equipment I built!
Uh no I'm not on drugs why do you ask?
Funny enough a router collecting this data near a busy enough highway can bog itself down by collecting unique Wi-Fi identifiers from all the passing cars' networks, not to mention all the hotspots on passing commuter trains.
It never occurs to router makers a static base could see a million Wi-Fi networks come and go every week.