At the core of such tracking is the MAC address, a unique identification number tied to each device. Devices looking for a Wi-Fi network send out their MAC address to identify themselves. Wireless routers receive the signals—and addresses—even if a connection is never made. Companies like Euclid or its peer Turnstyle Solutions use the data to track footfall in stores, how people move about in shops, how long they linger in certain sections, and how often they return. Store-owners use the information to
target shoppers with offers (paywall) or to move high-value items to highly-trafficked parts of the shop, among other things.
