Are you serious?
Deadly serious. Walk past my home made system and its better than evens that I could find your home wifi name. Put that into a war driving website and I could probably find your house. I have done this to test the concept.
Shops use anonymised versions of this to see how people walk about the store. Where they linger, where they rush, how long they spend on site. Putting something slightly different to your normal purchase in a place that you are known to spend time means they might sell it to you. Loyalty cards have nothing to do with loyalty, it's all about profiling the customer.
Tfl use it to read passenger movement on the underground. Oxford Street rubbish bins had a system, so they could track people along the shops.
My little system was written in Python, a language that kids learn, and runs on a £5 computer, with a few extra components. If I can do that, what could a professional criminal do?
If a WG or Sergei, had a probe monitoring system....