Ten days after the Supreme Court decided Carpenter v. United States — holding that the government’s acquisition of a criminal defendant’s historical cell phone records was a Fourth Amendment search — a group of experts gathered at Georgetown Law to discuss the implications with respect to location privacy.

“[These are] records maintained by phone companies, for all of our phones, detailing which cell towers are communicating with cell phones as users move about and use their phones,” explained Laura Moy, deputy director of the Center on Privacy and Technology at Georgetown Law. “In a 5-4 [decision], the Court held that yes, the government must get a warrant to obtain those records.”

Moy, a privacy advocate who once analyzed cell site location information at the Manhattan District Attorney’s office, described how prosecutors were using that information at the time. “You’ll hear a lot today about what cell site location is, what it does and can be used to do, how it has been used by law enforcement, and how it is likely to be used in the future.”

Dr. Sibren Isaacman of Loyola University in Maryland provided a technical primer on cell site location information. While the records are powerful in terms of providing information and evidence to law enforcement, there are “significant weaknesses.”“These locations are of towers, not of phones….” he said. “Cell site location information is not a GPS trace.”

Alvaro Bedoya, the founding executive director of the Center on Privacy and Technology, led a panel looking at the big picture implications of Carpenter. Nathan Wessler, an attorney from the American Civil Liberties Union who argued the case for the petitioner Carpenter, called the decision “earth shaking.”

“It creates a tremendous space moving forward to more adequately protect the kinds of sensitive information that we can’t avoid revealing about ourselves today…” he said. “The Court was very cognizant of the need to change and update and adapt our understanding of Fourth Amendment protections to take account of changing technologies.”

“Persons, houses, papers and effects”

Professor Laura Donohue, “one of the nation’s foremost Fourth Amendment scholars” whose work was cited five times in the dissenting opinion by Justice Clarence Thomas, said that while the majority reached the right result, the decision raises many questions.

“While I think that this case did reach the right conclusions — there is a Fourth Amendment interest in cell site location information — I am deeply concerned about the way in which the decision was reached. We are left with tons of questions…they put justices in a policy role, because it puts the courts in the position of deciding these seven factors that they laid out,” Donohue said. “You’re left with the question, what makes something a distinct category of information? How do you determine which side of the line you are on? If you are on the wrong side of the line, how much information is too much information or not? How much weight do you give each of the factors? Which factors count more than the others, etc. In short, I think this is really one big mess, and although it reaches the right conclusion, it’s the reasoning.”

Regarding Justice Thomas’s dissent, Donohue says she was “in complete accord” — up to the point where he believes the majority reads Fourth Amendment language of “persons, houses, papers and effects” out of existence, if there is indeed a privacy interest in cell site location information.

“I don’t think that’s right,” she said. “I think all of us now have…a personal doppelganger that follows us around that looks like us, talks like us, walks like us, goes the same places that we go — that is our ‘person,’ that is a digital ‘person’ that follows us around, and I think you can understand persons in that sense. You can also understand ‘effects’ in this sense. At the time the Constitution was written, ‘effects’ included business records…I think this is an important opportunity to really ground that right in the original understanding of the Fourth Amendment.”