How an obscure cellphone tracking tool provides police 'mass surveillance on a budget'

Local law enforcement agencies from suburban Southern California to rural North Carolina have been using an obscure cellphone tracking tool, at times without search warrants, that gives them the power to follow people’s movements months back in time, according to public records and internal emails obtained by The Associated Press.
Read more: https://www.pbs.org/newshour/politics/how-an-obscure-cellphone-tracking-tool-provides-police-mass-surveillance-on-a-budget?source=Snapzu