Afaik these guys have a very well working solution based on WiFi signals http://www.walkbase.com http://www.walkbase.com They started with the "indoor location

Afaik these guys have a very well working solution based on WiFi signals http://www.walkbase.com http://www.walkbase.com They started with the "indoor location app for people" idea, but later found a business when the phones are just being tracked for store etc. layout optimization.