This is really big in the WiFi space. Aruba, Cisco, etc all market services to public places like malls where you throw in a huge public wifi network, and regardless of whether you connect or not, they can see phones looking for known network and track traffic patterns.
Malls can then see which stores have highest foot traffic on what days, etc. It's actually one of the things that justifies the expense for huge, expensive free wifi deployments. And it is used to more accurately price locations around malls.
The other alternatives to getting the same kind of data is security camera analytics. Sometimes literally someone just watching footage and taking notes on who they see and what kind of demographics, etc. Which is problematic in it's own right.