While the data that's collected is anonymous, it can follow shoppers' paths from store to store.
The goal is for stores to answer questions like: How many Nordstrom shoppers also stop at Starbucks? How long do most customers linger in Victoria's Secret? Are there unpopular spots in the mall that aren't being visited?
While U.S. malls have long tracked how crowds move throughout their stores, this is the first time they've used cell phones.
But obtaining that information comes with privacy concerns.
The management company of both malls, Forest City Commercial Management, says personal data is not being tracked.