Stores can see where you go by tracking your phone - Business - The Boston Globe

Data shopping

"Companies that provide ‘‘mobile location analytics’’ to retailers, grocery stores, airports, and others say they capture the MAC addresses of shoppers’ phones but then scramble them into different sets of numbers and letters to conceal the original addresses — a process called hashing. This is how they make the data they collect anonymous, they say.
The companies then analyze all of the information those hashed numbers provide as shoppers move from store to store in a mall, or department to department in a store. Mall managers could learn which stores are popular and which ones aren’t. A retailer could learn how long the lines are at a certain cash register, how long people have to wait — or whether more people visit on ‘‘sale’’ days."

Stores can see where you go by tracking your phone - Business - The Boston Globe