The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
In United States v. Jones, 1 the Court seemed to revitalize the significance of governmental trespass in determining whether a Fourth Amendment search has occurred. In Jones, the Court considered whether the attachment of a Global-Positioning-System (GPS) device to a car used by a suspected narcotics dealer and the monitoring of such device for twenty-eight days, constituted a search. Although the Court ruled unanimously that this month-long monitoring violated Jones’s rights, it splintered on the reasoning. A majority of the Court relied on the theory of common law trespass to find that the attachment of the device to the car represented a physical intrusion into Jones’s constitutionally protected
effect or private property. 2 While this holding obviated the need to assess the month-long tracking under Katz’s reasonable expectation of privacy test, five Justices, who concurred either with the majority opinion or concurred with the judgment, would have held that long-term GPS tracking can implicate an individual’s expectation of privacy. 3 Some have read these concurrences as partly premised on the idea that while government access to a small data set—for example, one trip in a vehicle—might not violate one’s expectation of privacy, aggregating a month’s worth of personal data allows the government to create a
mosaic about an individual’s personal life that violates that individual’s reasonable expectation of privacy. 4
The Court confirmed in Carpenter v. United States that the Fourth Amendment is implicated when government action violates individuals' "reasonable expectation of privacy in the whole of their physical movements," regardless of whether the challenged conduct constitutes a physical trespass.  5 The Court held that the government could not, without a warrant, access seven days of a defendant's cell-site location information, which is data that continuously tracks the location of a cell phone.  6 Observing that "historical cell-site records present even greater privacy concerns than the GPS monitoring of a vehicle we considered in Jones," the Court highlighted the continuing importance of the expectations-of-privacy test.  7 The Court acknowledged that it had previously declined to extend Fourth Amendment protection to information that a person had voluntarily given to a third party like a wireless carrier, but declined to extend that line of cases to "the qualitatively different category of cell-site records."  8