Elena Kagan Just Bolstered the Fourth Amendment in a Badly Needed Way

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 trivial in isolation. Yet together they produce something earlier generations of police officers could scarcely imagine, which is a detailed reconstruction of an individual’s life. The law, however, has often struggled to account for that reality.

The genius of Kagan’s opinion is that she refuses the invitation. Rather than beginning with geofence warrants, she begins with first principles. The Fourth Amendment exists, she writes, to protect “the privacies of life” and to guard against “too permeating police surveillance.” This is the framework through which every technological question must now be understood. The constitutional inquiry is not whether a surveillance technique looks unfamiliar to 18^th-century judges, but it is whether technological innovation has given government access to precisely the sort of observational power the Fourth Amendment was designed to restrain.

That framing matters because the government attempted to portray Carpenter v. United States, the court’s landmark digital-privacy decision, as a narrow one. In that case, the court held that acquiring seven days of historical cell-site location information constituted a search requiring a warrant. The government effectively argued that Carpenter turned on quantity. Today, the court rejected that reading. Again and again, Kagan reminds readers that Carpenter was never fundamentally about seven days. It was about what location information reveals. Cellphone location records expose not simply where a person traveled, but how she lives. They reconstruct patterns of association that no human surveillance team could realistically assemble. And so their constitutional significance lies in their character, not merely their duration.

That point allows Kagan to make what may be the opinion’s most consequential doctrinal move. She expressly rejects the notion of Fourth Amendment protections somehow “kicking in” only after surveillance becomes sufficiently extensive or “goes too far.” Constitutional rights, she explains, do not operate on a sliding scale where more intrusion gradually transforms into a search. Either the government has invaded a protected privacy interest or it has not. Once the Fourth Amendment applies, it applies. There is no constitutional stopwatch measuring when surveillance becomes objectionable enough to matter.

That seemingly technical point has implications far beyond geofence warrants. Indeed, one of the striking features of the majority opinion is how persistently it resists artificial distinctions. The government argues that Google’s Location History differs from the cell-site records in Carpenter. Kagan responds that Location History is, if anything, even more revealing because it records a person’s location roughly every two minutes rather than whenever a phone connects to a cellular tower. It can identify locations within approximately 20 meters and can even estimate elevation, revealing which floor of a building someone occupies. If Carpenter protected the less revealing technology, the majority reasons, it necessarily protects the more revealing one.

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Nor does the court permit the government to divide privacy according to which company possesses the information. This portion of the opinion deserves far more attention than it will likely receive. For decades, Fourth Amendment doctrine has rested uneasily upon the so-called third-party doctrine, the proposition that information voluntarily shared with someone else generally loses constitutional protection. For bank records, telephone numbers, and business documents, for example, once shared, privacy largely disappears. Digital life has exposed the limits of that framework.

The majority no longer treats cloud providers primarily as recipients of information and instead recognizes how they increasingly resemble custodians of a person’s digital papers and effects.

That shift becomes even clearer when the court addresses voluntariness. The government insisted that users affirmatively enabled Location History and therefore knowingly exposed their information. Kagan refuses to treat smartphone use as a series of isolated contractual decisions. She instead asks how people actually use modern technology. Google repeatedly encourages users to activate Location History. Android devices warn that certain functions may not operate correctly otherwise. Most users never learn how frequently their locations are recorded or how extraordinarily detailed those records become. More fundamentally, nearly every smartphone function requires some affirmative permission somewhere along the way. If every click to enable an app or service amounted to surrendering Fourth Amendment protection, constitutional privacy would steadily evaporate as technology became more sophisticated.

Chatrie also demonstrates how digital surveillance increasingly reaches information people plainly regard as their own even when no traditional property concept neatly captures the intrusion. The majority sees constitutional privacy as capable of adapting to technological change without abandoning first principles.

Justice Samuel Alito’s dissent reflects a different concern altogether. He worries that the majority’s reasoning lacks administrable limits. If two hours of location information qualifies as a search, where exactly does the constitutional boundary lie? The question is fair. But it is also one the majority deliberately declines to answer in quantitative terms. That is because Kagan believes the question itself misunderstands the Fourth Amendment. Constitutional rights are not measured by how many minutes of surveillance government seeks to conduct.

The Fourth Amendment, the majority reminds us, cannot be atomized. Constitutional privacy is not lost because the government chooses to invade it one fragment at a time.

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