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Privacy Tracker | Constitution v Congress: Carpenter v United States Related reading: Reading the tea leaves in Carpenter v US



In a groundbreaking decision last week, the United States Supreme Court in Carpenter v. United States held in a 5-4 ruling that the Fourth Amendment to the U.S. Constitution requires the government to obtain a warrant — and not merely a subpoena under the Stored Communications Act — to acquire cell site location information (here called CSLI) held by a wireless communications company about its customer.

In so doing, the court acknowledged privacy interests in a cellphone’s persistent and constant generation of location data and found that such interests are not waived by involuntarily sharing that data with the wireless company. 


Police began investigating Timothy Carpenter in 2011 in connection with a string of store robberies in Detroit, Michigan. Carpenter’s accomplices had disclosed his name and cellphone to investigators, who obtained a subpoena under the SCA to compel Carpenter’s cell service providers (Metro PCS and Sprint) to turn over his CSLI for the four-month period when the robberies occurred.

To obtain a subpoena under the SCA, the police must offer “specific and articulable facts showing there are reasonable grounds to believe” the records sought are “relevant and material to an ongoing criminal investigation.”

After Carpenter’s trial, in which his location information during the robberies was used as evidence against him, Carpenter appealed his conviction, arguing that the CSLI collection required a warrant, not a mere subpoena.

Fourth Amendment to the US Constitution

Government surveillance is limited not just by laws passed by Congress but by the principles articulated in the Fourth Amendment, adopted “to safeguard the privacy and security of individ­uals against arbitrary invasions by governmental offi­cials.” The Fourth Amendment protects the “right of the people to be secure in their persons, houses, papers and effects, against unreasonable searches and seizures.” The government may acquire information but only with an issued warrant based upon probable cause that a crime has been committed or is imminent — a higher standard than the “reasonable grounds” required under the SCA.

In determining whether the Fourth Amendment applies to information collection activities, the U.S. Supreme Court must decide if the government has engaged in a “search” of “persons, houses, papers and effects.” Over the years, the court has expanded the definition of “search” beyond a physical invasion of a person’s body or property to include remote information collection facilitated by technological innovation. In each case, however, the court must determine whether the criminal suspect has a reasonable expectation of privacy in that information. Activities and communications carried on in public have not been considered private, nor has information voluntarily shared with third parties — such as, for example, records of phone calls (numbers dialed, time of call, etcetera) disclosed to the phone company, or corporate tax and payroll ledgers.

Because technological innovation permits ever-increasing data collection, the court is frequently called upon to evaluate whether the balance between government surveillance and individual privacy has swung too far to the government’s advantage. In the court’s words, the Fourth Amendment’s aim to protect “the privacies of life” requires placing “obstacles in the way of too permeating police surveillance.”

Here, the court for the first time evaluated whether a person has a reasonable expectation of privacy in CSLI – gathered remotely by a business of which the criminal suspect is a customer.

Tireless and absolute surveillance

In Carpenter v. United States, the court examined two lines of cases, the first relating to expectations of privacy in physical location information and the second exploring the limits of the “third party doctrine,” which provides that one has no reasonable expectation of privacy in information voluntarily disclosed to third parties.

Under the first line of cases, the court summarized that a person does not lose Fourth Amendment privacy protections “by venturing into the public sphere” and has a “reasonable expectation of privacy in the whole of their physical movements.” Cellphone location mapping over multiple days provides “an intimate window into a person’s life” (beyond mere movements) to encompass “familial, political, professional, religious, and sexual associations” — the ultimate “privacies of life.” What is more, “cell phone tracking is remarkably easy, cheap, and efficient.” The device itself — unlike the automobiles tracked in prior cases — “faithfully follows its owner beyond public thor­oughfares and into private residences, doctor’s offices, political headquarters, and other potentially revealing locales.” Tracking cellphone location allows the government “nearly perfect surveillance” not just in real time but retrospectively, when the government acquires records dating back several days, weeks or even years to reveal information previously “unknowable.”

The second line of cases involved the third-party doctrine, in which a company’s business records — in this case, the cell service provider — are not considered the customer’s own private information. This powerful doctrine has proved instrumental in government investigation techniques throughout history but particularly in the information age. It stems, at least in part, “from the notion that an individual has a reduced expectation of privacy in information shared with another.” The government had acquired Carpenter’s information as business records of his cell service providers via a subpoena issued by a magistrate judge pursuant to federal law — the Stored Communications Act.

According to the dissenting justices, these factors weighed most heavily in finding that Carpenter had no reasonable expectations of privacy in his CSLI and the government was not required to obtain a warrant. As Justice Kennedy noted in a dissent joined by Justices Alito and Thomas (Justice Gorsuch dissented separately), “customers do not create the records; they have no say in whether or for how long the records are stored; and they cannot require the records to be modified or de­stroyed.” What is more, Americans show no expectation of privacy in their daily movements and behaviors: “Millions of Americans choose to share their location on a daily basis, whether by using a variety of location-based services on their phones, or by sharing their location with friends and the public at large via social media.” Indeed, the dissent argued that burdening the government beyond obtaining a subpoena under the SCA poses a danger to society by limiting police powers to investigate and halt ongoing crimes.

The majority opinion, written by Justice Roberts, disagreed, noting that, “CSLI is an entirely different species of business record — something that implicates basic Fourth Amendment concerns about arbi­trary government power much more directly than corpo­rate tax or payroll ledgers.” A cell phone service provider, moreover, is “unlike the nosy neighbor who keeps an eye on comings and goings;” it is “ever alert,” and its memory is “nearly infallible.” Personal information is not truly “shared” voluntarily because the cell phone is “such a pervasive and insistent part of daily life that carrying one is indispensable to participation in modern society.”

According, the court held, because of the depth, breadth, and comprehensive reach of CSLI, its “deeply revealing nature,” and “the inescapable and automatic nature of its collection,” the government must seek a warrant notwithstanding the third party doctrine unless responding to “an ongoing emergency.”


The Carpenter case curtails government surveillance activities in the information age more than any prior opinion. It underscores the Fourth Amendment’s role in balancing society’s security interests against individual privacy rights, and it supports the judiciary’s role in ensuring privacy rights even when Congress has chosen to limit them.

Photo credit: dog97209 US Supreme Court Washington DC via photopin (license)

1 Comment

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  • comment Jessica Berger • Jun 27, 2018
    Carpenter v. United States potentiates the return to freedom of movement without government surveillance.  It sets the precedent to dismantle license plate scanners and motorway surveillance cameras because they trammel 4th Amendment Rights.  Removing these intrusive technologies from our roads will create jobs through the rehiring of toll booth operators.  We will then be free to travel again without our movements being tracked.  Great article Ms. Heimes!