Riley v. California, Explained

For decades, the "search incident to arrest" doctrine let police search whatever an arrestee was carrying, a wallet, a cigarette pack, a bag, without getting a warrant first. The justification was straightforward: officers need to check for weapons and stop evidence from being destroyed. Riley v. California asked whether that same logic applies to a smartphone, and the Court said no.

Why a phone is not a wallet

The case actually consolidated two separate arrests, one from a traffic stop that led to a search turning up gang-related evidence, the other from a drug-sale arrest. In both, police searched the arrestee's phone without a warrant. The government argued phones were no different from other physical objects that courts had long allowed police to search incident to arrest under the older United States v. Robinson line of cases. The Court rejected the analogy. Modern smartphones, the opinion reasoned, hold "a digital record of nearly every aspect of people's lives," from photos and messages to browsing history and location data, in a volume and variety that no physical object carried in a pocket comes close to matching. Searching a phone incident to arrest, the Court held, is nothing like searching a wallet.

What stands out about Riley is that it was unanimous on the bottom-line rule, decided 9 to 0 with Chief Justice Roberts writing for the Court and Justice Alito concurring separately in the judgment. Fourth Amendment cases are frequently split 5 to 4. Unanimity here signaled broad, cross-ideological agreement that cell phones are different in kind from the physical items the old search-incident-to-arrest rule was built around.

Carpenter extends the same idea to location history

Four years later, Carpenter v. United States pushed the same "digital is different" reasoning into a new area: historical cell-site location information, the record a wireless carrier keeps of which towers a phone connects to over time. Investigators had obtained 12,898 location points on Carpenter covering 127 days, using a court order under the Stored Communications Act rather than a warrant. The Supreme Court held that order was not enough. Absent a recognized exception, it said, "the Government's obligation is a familiar one, get a warrant," supported by probable cause.

That result cut against an older idea in Fourth Amendment law called the third-party doctrine, which generally lets police access records a person has voluntarily shared with a business, like a bank or a phone company, without a warrant. The Court in Carpenter treated location history as different enough in scope and sensitivity to require a warrant anyway, but it was careful to say it was not disturbing the third-party doctrine's older cases, and it left real-time tracking, security cameras, and other kinds of business records for another day.

Real landmarks, unsettled edges

Both decisions are widely treated as pro-privacy landmarks, but neither was free of disagreement about scope. Justice Alito agreed with the result in Riley but warned that a bright-line, categorical rule could create odd asymmetries, treating physical copies of information differently from digital copies of the same thing, and suggested legislatures might be better positioned than courts to draw some of these lines. Carpenter drew four separate dissents, with the dissenting justices raising concerns about eroding the third-party doctrine and doubting that the majority's reasoning about aggregated data gives lower courts a predictable rule to apply. The headline holdings in both cases are settled law. Exactly how far the underlying reasoning stretches, to shorter time windows, to real-time tracking, to other categories of business records, is still being worked out in the lower courts.