There are API’s you can buy monthly access to, on the order of 10-30k a month, that allow you to effectively ping and track almost any MAC address. Its a simple process of geofencing a couple locations and a bit of process of elimination to develop effectively passive tracking on just about anyone. Expect agencies to be buying this data.

I’m not sure who needs to know this but if you are doing sensitive work with vulnerable people, or know people who are, communicate this to them.