I once worked for a company that was producing a (cutting-edge at the time) system to sniff MAC addresses of mobile phones in a building etc, and create heat ma

I once worked for a company that was producing a (cutting-edge at the time) system to sniff MAC addresses of mobile phones in a building etc, and create heat maps of physical traffic. Combined with their other product, which was a crm-type of thing that also handled web analytics and so forth, it allowed us to see if a client's online marketing actually turned into real conversions. It was quite interesting, if a little bit on the legally-grey edge of things. I don't know how far it's progressed in the several years since I was there, but the product is called Blix: https://www.getblix.com/ https://www.getblix.com/