Good context and background in this WSJ piece about what appears to be the escalating practice of law enforcement in stealth mode tracking people via their cellphones. A case now before the U.S. Supreme Court should provide some clarity on its legality and whether search warrants are needed. 

The use of cellphone tracking by authorities is among the most common types of electronic surveillance, exceeding wiretaps and the use of GPS tracking, according to a survey of local, state and federal authorities by The Wall Street Journal. The widening practice also presents one of the biggest privacy questions in a generation: Do police need a search warrant to follow a person’s minute-by-minute movements using satellite or cellphone technology?

Image below from the WSJ story: