Attention, Shoppers - Store Is Tracking Your Cell - NYTimes.com

Shopper instrumentation

"RetailNext, based in San Jose, Calif., adds data from shoppers’ smartphones to deduce even more specific patterns. If a shopper’s phone is set to look for Wi-Fi networks, a store that offers Wi-Fi can pinpoint where the shopper is in the store, within a 10-foot radius, even if the shopper does not connect to the network, said Tim Callan, RetailNext’s chief marketing officer.
The store can also recognize returning shoppers, because mobile devices send unique identification codes when they search for networks. That means stores can now tell how repeat customers behave and the average time between visits."

Attention, Shoppers - Store Is Tracking Your Cell - NYTimes.com