This is part of Opinionpalooza, Slate’s coverage of the major decisions from the Supreme Court. Keep up with all of our Supreme Court coverage and analysis by signing up for weekly email roundups. The best way to support our work—and unlock exclusive legal analysis—is by joining Slate Plus. (If you are already a member, consider a donation or merch!)

The government’s argument in Chatrie v. United States was modest. The police didn’t obtain months of location data. Only two hours. They didn’t seek everyone’s identity immediately. At first, Google produced only anonymized information. They didn’t physically follow anyone. They simply asked Google for data it already possessed. Nor, the government emphasized, was this information collected automatically by a cellular provider. Users had chosen to enable Google’s Location History feature.

Each fact, standing alone, seemed capable of narrowing the constitutional question. Taken together, they formed the government’s central theory of the case: Whatever happened here was too limited, too incremental, too voluntary to qualify as a Fourth Amendment search.Justice Elena Kagan’s majority opinion on Monday dismantles that theory piece by piece. But the decision’s significance extends well beyond geofence warrants or Google’s Location History. At its core, the court’s split ruling in Chatrie rejects an increasingly common way of thinking about constitutional privacy. The government wanted the court to evaluate surveillance one fragment at a time. Kagan insists that the Fourth Amendment cannot be defeated by slicing invasions of privacy into pieces small enough to appear constitutionally insignificant.

That insight is what makes Chatrie one of the court’s most important Fourth Amendment decisions in years. For years, digital surveillance has advanced through accumulation. No single technology appears revolutionary. One GPS coordinate discloses almost nothing. One Wi-Fi connection says little. One Bluetooth signal, one app permission, one search-history entry, one fitness-tracker reading, each appears........

© Slate