The Massachusetts Supreme Judicial Court has ruled, in Commonwealth v. Estabrook, that police must obtain a warrant if they request historical cell-site location information (CSLI) from cell-phone service providers for a period of more than six hours, but that a warrant is not required for a period of six hours or less.  The decision was based on the Massachusetts Constitution, so its application is limited to the Bay State.  Nevertheless, the court’s decision to establish a “bright-line rule,” as arbitrary as it may seem, may have some influence on federal courts, which have been divided over whether the Fourth Amendment to the U.S. Constitution requires a warrant for CSLI.