"First, it determined that under the Supreme Court’s landmark ruling in Carpenter v. United States, individuals have a reasonable expectation of privacy in the location data implicated by geofence warrants… Second, the court found that even though investigators seek warrants for geofence location data, these searches are inherently unconstitutional… "
A geofence is an imaginary boundary around a location. If police get a ‘geofence warrant’, they can request a list of all phone#'s (and so their owners) that were in that area for a particular period of time. The court ruled this is too invasive for innocent people in that area.