After spending months sifting through the data, tracking the movements of people across the country and speaking with dozens of data companies, technologists, lawyers and academics who study this field, we feel the same sense of alarm. In the cities that the data file covers, it tracks people from nearly every neighborhood and block, whether they live in mobile homes in Alexandria, Va., or luxury towers in Manhattan.
One search turned up more than a dozen people visiting the Playboy Mansion, some overnight. Without much effort we spotted visitors to the estates of Johnny Depp, Tiger Woods and Arnold Schwarzenegger, connecting the devices’ owners to the residences indefinitely.