Master The Supreme Court held that obtaining historical cell-site location information (CSLI) from a wireless carrier is a Fourth Amendment search that generally requires a warrant supported by probable cause. with this comprehensive case brief.
Carpenter v. United States is the Supreme Court’s landmark decision adapting traditional Fourth Amendment doctrine to the realities of the digital age. The case addresses whether the government may obtain a person’s historical cell-site location information (CSLI) from a wireless carrier without a warrant. Because CSLI can reveal a comprehensive chronicle of a person’s movements over time, the case tests the limits of the third‑party doctrine forged in Smith v. Maryland and United States v. Miller, which had allowed the government to obtain certain business records held by third parties without a warrant.
In a 5–4 decision authored by Chief Justice Roberts, the Court held that individuals maintain a reasonable expectation of privacy in the record of their physical movements captured through CSLI and that the government’s acquisition of such records is a search under the Fourth Amendment. The ruling is expressly narrow but consequential: it requires law enforcement to secure a warrant supported by probable cause before obtaining historical CSLI in the run of cases, while preserving familiar exceptions like exigent circumstances and leaving unresolved questions about real-time tracking and tower dumps.
585 U.S. ___, 138 S. Ct. 2206, 201 L. Ed. 2d 507 (2018) (U.S. Supreme Court)
Federal agents investigated a series of armed robberies of RadioShack and T‑Mobile stores in Michigan and Ohio. After arresting participants, agents identified Timothy Carpenter as a suspect and, using orders issued under the Stored Communications Act (SCA), 18 U.S.C. § 2703(d), compelled Carpenter’s wireless carriers (including MetroPCS and Sprint) to disclose historical cell-site location information associated with his phones. The § 2703(d) standard requires "specific and articulable facts" showing reasonable grounds to believe the records are relevant and material to an ongoing investigation—short of probable cause. The government obtained, among other records, 127 days of CSLI from MetroPCS, yielding 12,898 location points (about 101 points per day), which placed Carpenter’s phone near several robbery locations at pertinent times. Carpenter moved to suppress, arguing the Fourth Amendment required a warrant. The district court denied the motion, the jury convicted on robbery and firearms counts, and the Sixth Circuit affirmed, reasoning under Smith and Miller that Carpenter lacked a reasonable expectation of privacy in records voluntarily conveyed to third-party carriers.
Does the government’s acquisition of historical cell-site location information from a wireless carrier without a warrant supported by probable cause constitute a search under the Fourth Amendment?
An individual maintains a reasonable expectation of privacy in the record of his physical movements as captured through historical cell-site location information. Government acquisition of such CSLI from a wireless carrier is a Fourth Amendment search that generally requires a warrant supported by probable cause. The third‑party doctrine of Smith v. Maryland and United States v. Miller does not extend to the unique, deeply revealing, and involuntarily generated nature of CSLI. Traditional exceptions to the warrant requirement, including exigent circumstances, remain available, and the Court’s holding is narrowly focused on historical CSLI rather than other forms of business records or real-time tracking.
Yes. Obtaining historical CSLI from a wireless carrier is a Fourth Amendment search. In the absence of an applicable exception, the government must secure a warrant supported by probable cause; an SCA § 2703(d) order is insufficient.
The Court began from Katz’s reasonable-expectation-of-privacy test, emphasizing that the Amendment protects people, not places, and that technological change can amplify privacy interests. CSLI is qualitatively different from the limited business records in Smith and Miller: it provides an exhaustive chronicle of a person’s past movements, often over months, with a precision that can reveal the privacies of life—home, work, associations, religious practices, medical visits—similar in sensitivity to GPS data discussed in United States v. Jones and the smartphone contents addressed in Riley v. California. Unlike the pen register in Smith (dialed numbers) or the bank records in Miller (financial documents), CSLI is not truly “voluntarily” conveyed. A cell phone continuously and automatically logs data with carriers simply by being powered on and connected to the network; carrying a phone is essential to modern life, so users cannot reasonably be said to opt in to pervasive tracking. The Court rejected the government’s reliance on the third‑party doctrine, limiting Smith and Miller to their facts and declining to create a categorical rule that any information held by a third party loses Fourth Amendment protection. While the records are technically held by carriers, the depth, breadth, and retrospective nature of CSLI implicate a strong privacy interest. The majority characterized its holding as narrow: it applies to historical CSLI and does not call into question conventional subpoenas for less sensitive business records, nor does it decide issues involving real-time CSLI, tower dumps, or national security. It also recognized that established exceptions like exigent circumstances (e.g., bomb threats, active shootings, child abductions) permit warrantless access in emergencies. Because the government proceeded under the SCA’s lesser “specific and articulable facts” standard, the acquisition here was unconstitutional absent a warrant. (The Court did not resolve the good-faith issue, leaving remedial questions for remand.) Dissents argued that Smith and Miller control because the records belong to carriers; that CSLI is simply business data subject to subpoena; that line-drawing is difficult and best left to legislatures; and, in one view, that the focus should return to property-based or positive-law baselines. The majority, however, concluded that respecting reasonable expectations of privacy in an era of ubiquitous digital tracking is essential to preserving the Amendment’s core protection against intrusive government surveillance.
Carpenter is foundational for understanding how Fourth Amendment doctrine adapts to digital technologies. It limits the third‑party doctrine by recognizing a reasonable expectation of privacy in certain highly revealing data held by third parties, and it establishes that historical CSLI is protected information that generally requires a warrant. For students, the case is a critical node connecting Katz, Smith, Miller, Jones, and Riley, and it illustrates the Court’s willingness to craft technology-sensitive rules while preserving traditional exceptions and leaving room for case-by-case development on related questions (real-time tracking, tower dumps, metadata categories, and national security contexts).
No. The Court limited Smith and Miller to their facts and declined to extend the third‑party doctrine to CSLI. It held that the unique, pervasive, and involuntarily generated nature of CSLI distinguishes it from dialed numbers and bank records. Thus, Carpenter narrows the doctrine without overruling those precedents.
No. The decision is expressly narrow. It covers historical CSLI because of its uniquely revealing, comprehensive depiction of a person’s movements. Conventional business records that are less sensitive remain generally obtainable via subpoena. Courts will assess other digital categories case-by-case, considering sensitivity, voluntariness, depth, and pervasiveness.
The Court did not decide those issues. Carpenter concerns historical CSLI. The opinion leaves open whether real-time CSLI or so-called tower dumps (bulk acquisition of all devices connected to a tower during a time window) require a warrant. Related surveillance like GPS tracking is addressed in Jones (trespass-based and mosaic concerns), but Carpenter does not resolve every digital tracking method.
An SCA § 2703(d) order requires only "specific and articulable facts" showing reasonable grounds to believe the records are relevant and material to an ongoing investigation—a standard lower than probable cause. Carpenter holds that obtaining historical CSLI is a search, so the Fourth Amendment generally requires a warrant supported by probable cause, making the § 2703(d) orders inadequate.
Yes. The majority emphasized that traditional exceptions to the warrant requirement remain intact. In emergencies—such as bomb threats, active shooters, or child abductions—law enforcement may obtain CSLI without a warrant, subject to subsequent judicial review.
The Supreme Court reversed and remanded, leaving remedial issues unresolved. On remand, the Sixth Circuit applied the good-faith exception, concluding that officers relied on the SCA in objectively reasonable fashion at the time, so suppression was not required. As a result, Carpenter’s convictions were not vacated on remand.
Carpenter reshapes Fourth Amendment law for an era in which smartphones quietly generate rich location histories. By recognizing a reasonable expectation of privacy in historical CSLI, the Court requires warrants for this category of data and limits the reach of the third‑party doctrine, while preserving exigency and declining to opine on adjacent surveillance practices.
For practitioners and students, Carpenter is a touchstone for analyzing digital privacy questions: identify the nature of the data, assess voluntariness and intrusiveness, consider technological pervasiveness, and then apply Katz, Jones, Riley, and the third‑party doctrine in a calibrated manner. It signals an incremental, technology‑aware approach to privacy that will continue to shape criminal procedure and constitutional litigation.