(NYT) “Law enforcement tracking of cellphones, once the province mainly of federal agents, has become a powerful and widely used surveillance tool for local police officials, with hundreds of departments, large and small, often using it aggressively with little or no court oversight, documents show… . .
“But civil liberties advocates say the wider use of cell tracking raises legal and constitutional questions, particularly when the police act without judicial orders. While many departments require warrants to use phone tracking in nonemergencies, others claim broad discretion to get the records on their own, according to 5,500 pages of internal records obtained by the American Civil Liberties Union from 205 police departments nationwide.”

Map below from ACLU research and records requests.