Carpenter v. United States
The decision holding that acquisition of at least seven days of historical cell-site location information is a Fourth Amendment search.
Executive Summary
Federal investigators obtained Timothy Carpenter’s historical cell-site location information under the Stored Communications Act using court orders based on reasonable grounds rather than probable cause. The records placed his phone near several robberies and covered 127 days, producing thousands of location points.
The Supreme Court held that obtaining at least seven days of historical CSLI is a Fourth Amendment search. The government generally must obtain a warrant supported by probable cause. The majority declined to extend the third-party doctrine of Smith and Miller to the comprehensive record of physical movements created by cellphone use.
The Court emphasized the depth, breadth, and inescapable character of CSLI. Cellphones continuously connect to towers as a basic operational function, and carrying one is indispensable to participation in modern society. Users do not meaningfully volunteer a detailed chronicle of their movements in the traditional sense.
The opinion repeatedly described its holding as narrow. It did not address real-time CSLI, tower dumps, security cameras, business records generally, conventional surveillance, or all provider-held data. Even so, its reasoning reshaped digital privacy analysis and became central to geofence, ALPR, persistent-surveillance, and bulk-data disputes.
Historical Context
Smith and Miller supported the proposition that information voluntarily conveyed to a third party generally carries no reasonable expectation of privacy. Meanwhile, Jones exposed concern about long-term automated location tracking. Carpenter brought those lines together.
The Stored Communications Act permitted the government to obtain certain records through a statutory order requiring specific and articulable facts showing relevance to an investigation. The constitutional question was whether that lesser process was enough for a revealing historical location record.
Facts
A series of robberies targeted Radio Shack and T-Mobile stores in Ohio and Michigan. One participant confessed and provided phone numbers for accomplices. Prosecutors obtained orders requiring wireless carriers to produce transactional records for Carpenter’s phone.
The government received 12,898 location points spanning 127 days. An FBI agent mapped the records and testified that Carpenter’s phone was near robbery locations at relevant times. The data’s precision varied with tower density and network architecture, but it allowed retrospective reconstruction of movements.
Procedural History
Carpenter moved to suppress, arguing that the records were obtained without a warrant. The district court denied the motion, and the Sixth Circuit affirmed under the third-party doctrine. The Supreme Court reversed, holding the acquisition was a search.
Constitutional Question
Does government acquisition of at least seven days of historical cell-site location information from a wireless carrier constitute a Fourth Amendment search requiring a warrant?
Holding
Yes. A person maintains a legitimate expectation of privacy in the whole of physical movements captured through at least seven days of historical CSLI. The government generally must obtain a warrant supported by probable cause before acquiring that record.
Court’s Reasoning
Chief Justice Roberts described CSLI as qualitatively different from the limited business records in earlier cases. It provides a detailed, effortless, and retrospective chronicle of where a person has been. Because carriers retain records, government can travel back in time to reconstruct movements without deploying officers in advance.
The majority drew on the concerns expressed in Jones. Public travel is observable in isolated moments, but comprehensive aggregation can reveal the privacies of life. The cost and practical limitations of traditional surveillance historically constrained government; digital records remove those constraints.
The Court also rejected a simplistic voluntary-exposure rationale. Phones generate CSLI automatically by connecting to the network. Users do not affirmatively choose to disclose each location point, and avoiding the technology is not a realistic condition of modern participation.
The opinion balanced privacy with legitimate investigative needs. It preserved exigent-circumstances doctrine and recognized that warrants can often be obtained efficiently. It also declined to invalidate less revealing forms of business-record collection.
Separate Opinions
Justice Kennedy dissented, joined by Justices Thomas and Alito, arguing that CSLI was the carrier’s business record and that the majority departed from settled property and third-party principles. Justice Thomas separately criticized the reasonable-expectation framework.
Justice Alito warned that the decision could destabilize subpoenas and investigative access to third-party records. Justice Gorsuch argued that privacy analysis should explore positive-law and property-based interests in digital records, foreshadowing later debates about user ownership and control.
Continuing Significance
Carpenter is the principal modern case for location privacy and data aggregation. Courts use its factors—comprehensiveness, precision, duration, automatic generation, retrospective reach, and practical necessity—to evaluate new datasets.
Agencies should not treat seven days as a safe harbor or bright line. Shorter periods may still be highly precise or revealing, and state law may be more protective. Warrants should define accounts or devices, time and geography, data fields, minimization, return procedures, and handling of non-target data.
What Carpenter Does Not Hold
Carpenter does not eliminate the third-party doctrine. It does not announce a general right to privacy in all digital records. It does not decide real-time tracking, tower dumps, geofence warrants, security-camera footage, or conventional visual surveillance. It also preserves exigency and other established exceptions.
Shield Practice Notes
Use a warrant
For historical or real-time location records, default to a probable-cause warrant unless controlling law clearly permits another process.
Define the dataset
Specify the data type, source, precision, interval, retention period, and whether the provider will return derived or raw location information.
Minimization
Limit time and scope, segregate nonresponsive information, and document deletion or retention decisions for non-target data.
Explain necessity
Show why the requested period and geography are tied to the offense rather than asking for the maximum technically available history.
Key Quotations
Primary References
- Carpenter v. United States, 585 U.S. 296 (2018).
- Smith v. Maryland, 442 U.S. 735 (1979).
- United States v. Jones, 565 U.S. 400 (2012).