Your apps know where you were last night, and they're not keeping it secret

The millions of dots on the map trace highways, side streets and bike trails — each one following the path of an anonymous cellphone user. One path tracks someone from a home outside Newark to a nearby Planned Parenthood, remaining there for more than an hour. Another represents a person who travels with the mayor of New York during the day and returns to Long Island at night. Yet another leaves a house in upstate New York at 7 am and travels to a middle school 14 miles away, staying until late afternoon each school day. 

Only one person makes that trip: Lisa Magrin, a 46-year-old math teacher. Her smartphone goes with her. An app on the device gathered her location information, which was then sold without her knowledge. It recorded her whereabouts as often as every two seconds, according to a database of more than a million phones in the New York area. While Magrin’s identity was not disclosed in those records, The Times was able to easily connect her to that dot. The app tracked her as she went to a Weight Watchers meeting. It followed her hiking with her dog and staying at her ex-boyfriend’s home, information she found disturbing. “It’s the thought of people finding out those intimate details that you don’t want people to know,” said Magrin, who allowed The Times to review her location data.

Like many consumers, Magrin knew that apps could track people’s movements. But as smartphones have become ubiquitous and technology more accurate, an industry of snooping on people’s daily habits has spread and grown more intrusive. 

At least 75 companies receive anonymous, precise location data from apps whose users enable location services to get local news and weather, The Times found. Several of those businesses claim to track up to 200 million mobile devices in the  US — about half those in use last year. The database reviewed by The Times — a sample of information gathered in 2017  — reveals people’s travels in startling detail, accurate to within a few yards.