It's more invasive than that. I've seen MIT research using several WiFi routers to detect heart rate and respiration[1]. It's not too much of a leap to using it as a lie detector. A little more of a leap, and you get cameras watching window shoppers, plus some Machine Learning, to get a system able to detect which items excite which shoppers when they look at the items (via heart rate and respiration). Could also maybe be used to detect shoplifters.
[1] https://www.medgadget.com/2014/06/mits-wifi-system-detects-p...