There are already solutions that do this using your phone's wifi: https://www.washingtonpost.com/blogs/the-switch/wp/2013/10/19/how-stores-use-your-phones-wifi-

There are already solutions that do this using your phone's wifi: https://www.washingtonpost.com/blogs/the-switch/wp/2013/10/19/how-stores-use-your-phones-wifi-to-track-your-shopping-habits/ https://www.washingtonpost.com/blogs/the-switch/wp/2013/10/1...