The New York Times, exposed in detail how you can be tracked if you posses a smartphone real-time, without your knowledge or permission. The publication puts forward a great example: tracking the President of the United States using the movements of his Secret Service agents, alone with other government officials.
Actually, it is very troubling that they can track and identify Secret Service agents and other people then Trump himself. The Presidents schedule is often made public, he is well protected… who’s watching the watchers though? Apparently, those who have the same data as NYT.