(Until recently I was the co-founder/CTO at RetailNext - we analyze shopper behavior in retail stores, primarily using computer vision but also using WiFi signa

(Until recently I was the co-founder/CTO at RetailNext - we analyze shopper behavior in retail stores, primarily using computer vision but also using WiFi signals and other methods.) WiFi signals contain a device MAC, which gives us a unique ID on the customer. This allows us to track repeat visits to a store, and even visits to different stores within the same retail chain. We can also track the WiFi "pings" from your device to see approximately how long you were in the store, whether you passed by the store without walking in, etc. Essentially the physical-world equivalent of data that google analytics provides you for your website. The type of data described above is not quite possible to obtain via video as face recognition is nowhere near as robust, certainly not when it needs to be done non-intrusively as in a retail environment. Video is still very useful however as it gives us 100% customer coverage - many customers still don't have smartphones, many that do keep WiFi turned off, many stores don't have WiFi APs, etc.