Here is the Court ruling (pdf)
In a major decision, the federal Fifth Circuit Court of Appeals held that geofence warrants are “categorically prohibited by the Fourth Amendment.”
The court found that geofence warrants constitute the sort of “general, exploratory rummaging” that the drafters of the Fourth Amendment intended to outlaw.
“The Electronc Frontier Foundation (EFF) applauds this decision because it is essential that every person feels like they can simply take their cell phone out into the world without the fear that they might end up a criminal suspect because their location data was swept up in open-ended digital dragnet,” the EFF says.
The new Fifth Circuit case, United States v. Smith, involved an armed robbery and assault of a US Postal Service worker at a post office in Mississippi in 2018. After several months of investigation, police had no identifiable suspects, so they obtained a geofence warrant covering a large geographic area around the post office for the hour surrounding the crime. Google responded to the warrant with information on several devices, ultimately leading police to the two defendants.
I’m under the impression that these sort of third-party warrants are often accompanied by a gag order. Which is why warrant canaries are a thing.