Carpenter v. United States
The Supreme Court ruled that police generally need a warrant to obtain someone's historical cell phone location records, rejecting the government's argument that a lower court order was enough because a phone company held the records.
The 5-4 decision recognizes that tracking a person's movements through cell phone data over many days is so revealing that it deserves the same constitutional protection as a search of a home, even though a private company created and stored the records.
How it got here: A federal magistrate approved court orders for the records; the district court denied Carpenter's motion to suppress; the Sixth Circuit affirmed his conviction, and he asked the Supreme Court to review.
The Case in Depth
What happened
After a string of armed robberies of Radio Shack and T-Mobile stores in Michigan and Ohio, the FBI identified Timothy Carpenter as a suspect using confessions and cell phone numbers from his accomplices. Prosecutors obtained months of Carpenter's cell-site location records from his wireless carriers, which tracked his phone's connections to nearby cell towers, and used that data at trial to place him near four of the robberies.
The question before the Court
Does police access to months of a person's cell phone location records, obtained from a phone company without a warrant, count as a search under the Fourth Amendment?
The Court's answer
Yes — the Court ruled that when the government obtains many days of a person's historical cell-site location records, it conducts a search under the Fourth Amendment, so it generally needs a warrant backed by probable cause. The Court reasoned that cell-site records create a detailed, retrospective log of someone's movements that the person never truly chooses to share, since phones generate this data automatically just by being on.
Because the government here relied only on the Stored Communications Act's lower "reasonable grounds" standard rather than a warrant, its collection of Carpenter's records was unconstitutional. The Court stressed its ruling is narrow, leaving open questions about real-time tracking, tower dumps, and security cameras, and said case-specific emergencies can still justify warrantless access.
Curious how the Court got there? See the step-by-step legal reasoning →
Why it matters
Police departments and federal investigators must now get a warrant backed by probable cause before pulling weeks or months of a suspect's cell-site location history, rather than relying on the lower legal bar in the Stored Communications Act. Cell phone users gain stronger protection over records that can reveal where they go to church, the doctor, or a protest.
What changes now
The case returns to the lower courts for further proceedings consistent with the ruling that the cell-site records were obtained through an unconstitutional search. The decision does not itself throw out Carpenter's conviction; courts below must decide what follows from the constitutional violation. The Court also left open how its ruling applies to real-time location tracking, tower dumps, and national security investigations.
What this does not decide
The Court called its ruling narrow: it does not address real-time cell phone tracking, "tower dumps" of everyone connected to a cell site, other business records that might reveal location, security cameras or other conventional surveillance tools, or cases involving national security or foreign affairs. It also does not disturb the general rule that other business records held by third parties get no Fourth Amendment protection.
Concurrences and dissents
Dissent — Justice Kennedy
“That distinction is illogical and will frustrate principled application of the Fourth Amendment in many routine yet vital law enforcement operations.”Kennedy's objection to the majority's line between cell-site records and other business records.
Justice Kennedy argued that cell-site records are no different from the bank and telephone records the Court already said get no Fourth Amendment protection, because the customer neither owns nor controls them. He warned the new rule is unprincipled, will hamstring routine investigations, and should have left this to Congress rather than inventing an arbitrary line at a set number of days.
Dissent — Justice Thomas
Justice Thomas rejected the entire 'reasonable expectation of privacy' framework from Katz v. United States as having no basis in the Fourth Amendment's text, arguing the case should instead turn on whose property was searched. Since the records belonged to the phone companies, not Carpenter, he would find no search occurred at all.
Dissent — Justice Alito
Justice Alito argued the majority wrongly treated a court order compelling a company to produce its own records the same as an actual physical search, and wrongly let Carpenter object to a search of someone else's property. He warned this would jeopardize subpoenas used throughout civil and criminal investigations nationwide.
Dissent — Justice Gorsuch
Justice Gorsuch argued the entire Katz privacy-expectations framework, including the third-party doctrine it spawned, is unmoored from the Constitution's text and produces unpredictable results. He suggested courts should instead ask whether records like cell-site data qualify as a person's 'papers' or 'effects' under property law, but concluded Carpenter had forfeited that argument by not raising it below.
How the Court got there
The legal reasoning, step by step
- The Court identified two lines of precedent bearing on the case: cases protecting a person's expectation of privacy in their physical movements (like GPS tracking), and cases holding that people give up privacy protection for information they voluntarily hand over to third parties, known as the third-party doctrine.
- The Court found that historical cell-site records combine the worst features of both categories: like GPS tracking, they create a detailed, encyclopedic record of someone's movements, but like third-party records, they are generated and stored by a phone company rather than the user.
- Rather than mechanically applying the third-party doctrine, the Court asked whether the third-party doctrine's usual justifications — reduced privacy interest and voluntary disclosure — actually hold up for this kind of data, and concluded they do not, because cell phones automatically generate location records just by being powered on, without any meaningful choice by the user.
- Because cell-site records can retroactively reconstruct years of a person's whereabouts with near-perfect precision and at almost no cost to the government, the Court held that accessing them invades a legitimate expectation of privacy in the whole of one's physical movements, making the third-party doctrine inapplicable here.
- Having found that this collection amounted to a Fourth Amendment search, the Court applied the ordinary rule that warrantless searches for evidence of crime are unreasonable unless a specific exception applies, and concluded that the reasonable-grounds standard in the Stored Communications Act falls well short of the probable-cause showing a warrant requires.
Doctrinal impact
Cases affected by this decision
Limits Smith v. Maryland (442 U. S. 735)
The Court declined to extend this ruling on phone records to cover detailed cell-site location data.
Limits United States v. Miller (425 U. S. 435)
The Court declined to extend this bank-records ruling's third-party doctrine to historical cell-site data.
Reaffirms United States v. Jones (565 U. S. 400)
The Court relied on concurring opinions in Jones recognizing privacy in the whole of one's movements.
Reaffirms Katz v. United States (389 U. S. 347)
The Court applied Katz's reasonable-expectation-of-privacy framework rather than reconsidering it.