Cookies are tracking our online behavior for advertising purposes, but a company specializing in retail analytics called Euclid, Inc. is moving that concept into real world shopping experiences.

Euclid uses open WiFi access points to track shopper behavior across stores: It does this by collecting the MAC address of smart phones as they passively connect to open networks while people shop, anonymizing the data, putting it into a giant database that then recognizes the device when it goes near any other Euclid customer’s network.