Location-tracking technology can now monitor people so precisely that retailers know, for instance, which customers visited a fitting room but never made it to the cash register. From there, retailers can serve custom ads on platforms like WeChat, Facebook and Google. Cosmose is one start-up using location-based tracking to help retail firms do just that. Tracking takes place through apps for which users have enabled location services (think weather, mapping, or ride-sharing apps). Seven apps have location tracking enabled on an average smartphone in China, according to Cosmose. The company said it’s tracked more than 1 billion smartphones, primarily in China, across 100,000 stores it works with. Its clients include Burberry, L’Oreal, Subway and Budweiser. Cosmose said it plans to expand its reach into the United States. Read more at CNBC.