While the justices unanimously agreed police violated a suspect's Fourth Amendment rights, the Court split on whether the government can track you without a device.
Last fall the Supreme Court heard a case concerning whether police in Washington DC were in violation of the Constitution when they tracked the car of a suspected drug dealer's wife using a GPS device they installed on the car. Today the Court decided that the police did violate the Fourth Amendment, which protects people from "unreasonable search and seizures" and it did so unanimously.
But that's about the extent of the Justices' agreement. They split among three different opinions, and that of the majority -- authored by Justice Scalia and signed by Chief Justice Roberts and Justices Kennedy, Thomas, and Sotomayor -- is as narrow as can be, resting on the specifics of this particular case but saying little as to whether GPS tracking is more broadly permissible. The government's act of physically attaching the device to the undercarriage of the car is a physical trespass, the Court held, something clearly prohibited by the Fourth Amendment as it was originally understood in the 18th century. But, and here is the decision's narrowness, it "may be that achieving the same result through electronic means, without an accompanying trespass, is an unconstitutional invasion of privacy. ... [The] present case does not require us to answer that question." Meaning, in the majority's opinion, the question of GPS tracking is still up in the air.
So it's possible that attaching something to a car is unconstitutional, but tracking their every move -- as long as you do not technically trespass while installing the device -- is just fine?
The real meat, for those interested in that question, comes in two concurring opinions, one from Justice Sotomayor (who also signed the majority's) and another authored by Justice Alito and signed by Justices Ginsburg, Breyer, and Kagan. The problem with Scalia's opinion, Alito writes, is that it overly relies on originalist reasoning -- that is, whether the case in question comports with the Fourth Amendment as the Framers meant it. But that interpretation of the Fourth Amendment -- one "based on 18th-century tort law" -- is insufficiently illuminating for what to do with today's technologies, technologies that allow for a level of tracking never imagined by James Madison and others.
As Alito writes, in one of the decision's most incisive passages, "In the pre-computer age, the greatest protections of privacy were neither constitutional nor statutory, but practical. ... The surveillance at issue in the case -- constant monitoring of the location of a vehicle for four weeks -- would have required a large team of agents, multiple vehicles, and perhaps aerial assistance. Only an investigation of unusual importance could have justified such an expenditure of law enforcement resources." Today, we need law to make up for the protections that technological difficulties once provided.
Alito goes on to say that the logical end of the Court's reasoning is a bit laughable. So it's possible that attaching something to a car is unconstitutional, but tracking their every move -- as long as you do not technically trespass while installing the device -- is just fine? This is why relying on 18th-century understandings of the Fourth Amendment fail to help us with modern questions.