Carpenter v. United States
The Supreme Court ruled that police generally need a warrant backed by probable cause before getting a person's historical cell phone location records from a wireless carrier, because pulling together months of someone's whereabouts amounts to a Fourth Amendment search.
The decision means a lower legal standard used for ordinary business records does not automatically apply to the detailed, comprehensive picture of a person's movements that cell-site data can reveal, even though a phone company technically owns those records.
“Our decision today is a narrow one.”
The majority stresses that its Fourth Amendment ruling on cell-site records is limited in scope.
How it got here: A federal trial court denied Carpenter's motion to suppress the cell-site records; the Sixth Circuit affirmed his conviction; the Supreme Court agreed to hear his appeal.
The Case in Depth
What happened
Timothy Carpenter was accused of helping rob a string of Radio Shack and T-Mobile stores in Michigan and Ohio. Investigators got his wireless carriers to hand over months of cell-site records showing which cell towers his phone connected to, producing thousands of location points. Prosecutors used maps built from that data at trial to place Carpenter's phone near four of the robberies when they happened.
The question before the Court
Does police access to months of cell phone location records, obtained without a warrant, count as a Fourth Amendment search?
The Court's answer
Yes — the Court ruled that when the government obtains an extensive record of someone's past cell phone location history, it has conducted a Fourth Amendment search, even though a wireless carrier technically owns those records. The Court reasoned that this kind of tracking reveals an all-encompassing picture of a person's movements, similar to the GPS monitoring it had flagged as concerning in an earlier case, and that this made the older rule about business records shared with companies too weak to apply here.
Because a search occurred, the government generally needed a warrant backed by probable cause, not the lower "reasonable grounds" showing the Stored Communications Act required. The Court limited its ruling to historical cell-site records like the ones at issue, leaving open how the rule applies to real-time tracking, bulk data requests, and other emerging technologies.
Curious how the Court got there? See the step-by-step legal reasoning →
Why it matters
Police and prosecutors nationwide who want an extended history of a suspect's cell phone location must now generally get a warrant instead of a lower-threshold court order. That makes it somewhat harder and slower for law enforcement to reconstruct a suspect's past movements, while giving ordinary cell phone users more legal protection over records their carriers hold about them.
What changes now
The case was sent back to the lower courts for further proceedings applying the new warrant requirement. The ruling is a final decision on the merits, not a temporary order, and it now governs how police across the country must obtain historical cell-site location records. The Court left several related questions open, including real-time tracking and bulk 'tower dump' requests, for future cases to resolve.
What this does not decide
The Court said its ruling is narrow: it does not address real-time cell phone tracking, bulk "tower dump" requests covering many people at once, security cameras or other conventional surveillance tools, other business records that might reveal location, or techniques used in foreign-affairs or national-security investigations.
Concurrences and dissents
Dissent — Justice Kennedy
“A person’s movements are not particularly private.”Kennedy's dissent disputes that location information deserves the strong privacy protection the majority gave it.
Justice Kennedy argued the Court should have applied Miller and Smith as written: because cell-site records are owned and controlled by the phone company, not the customer, obtaining them through court-approved compulsory process was not a search at all. He warned the new rule creates an unworkable line between cell-site records and equally revealing financial or telephone records, and would hamper legitimate investigations.
Dissent — Justice Thomas
Justice Thomas argued the case should turn on whether the records were Carpenter's property, not on an expectation-of-privacy test. He would abandon the Katz 'reasonable expectation of privacy' framework entirely, contending it lacks any basis in the Fourth Amendment's text and history and has produced unpredictable results, and would instead ask only whether the government searched the defendant's own papers or effects.
Dissent — Justice Alito
Justice Alito argued the majority wrongly treated a court order compelling a third party to produce documents as equivalent to an actual search of a person's home, when centuries of practice and precedent treat subpoenas differently and less strictly. He also argued Carpenter had no standing to object to a search of records owned by his carrier, since Fourth Amendment rights are personal and cannot be asserted over someone else's property.
Dissent — Justice Gorsuch
Justice Gorsuch rejected both the third-party doctrine and the Katz privacy-expectations test as poor foundations for Fourth Amendment law, arguing courts should instead ask whether records count as a person's own 'papers or effects' under positive law and property principles like bailment. He suggested Carpenter might have had a strong property-based claim to his cell-site data but had forfeited that argument by not raising it below.
How the Court got there
The legal reasoning, step by step
- The Court asked whether accessing historical cell-site records fits within two existing lines of Fourth Amendment cases: one protecting a person's expectation of privacy in their physical movements, and another (the 'third-party doctrine') holding that people generally have no privacy interest in records voluntarily shared with businesses like banks or phone companies.
- The Court found that cell-site tracking resembles the GPS monitoring it had flagged as troubling in United States v. Jones, because it is detailed, comprehensive, and effortlessly compiled, letting the government reconstruct a person's whereabouts over long stretches of time.
- The Court concluded that the third-party doctrine, developed for narrow records like bank statements and dialed phone numbers, should not automatically extend to cell-site data, because that data is far more revealing and is generated automatically just from carrying a phone, without any meaningful voluntary choice to share it.
- Because obtaining the records intruded on a legitimate expectation of privacy in the whole of a person's movements, the Court held that acquiring at least seven days' worth of historical cell-site records was a Fourth Amendment search.
- Since a search occurred, the Court applied the ordinary rule that warrantless searches for evidence of crime are typically unreasonable, and found that the Stored Communications Act's 'reasonable grounds' standard for court orders falls well short of the probable cause required for a warrant.
- The Court concluded that police must generally get a warrant before obtaining this kind of historical cell-site data, while leaving room for case-specific exceptions like emergencies.
Doctrinal impact
Cases affected by this decision
Limits Smith v. Maryland (442 U. S. 735)
The Court declined to extend Smith's rule that shared business records lack privacy protection to cell-site location data.
Limits United States v. Miller (425 U. S. 435)
The Court declined to extend Miller's third-party doctrine for bank records to cover comprehensive cell-site location records.
Reaffirms Katz v. United States (389 U. S. 347)
The Court relied on Katz's reasonable-expectation-of-privacy framework as the basis for finding a search occurred.