Author:Ohm, Paul

TABLE OF CONTENTS I. INTRODUCTION 358 II. THE NEW RULE OF CARPENTER 361 A. Carpenter's Broad New Rule 361 B. On Police Efficiency and Time Machines 366 C. What is the Carpenter Test? 369 1. First Factor: Deeply Revealing Nature 371 2. Second Factor: Depth, Breadth, 372 and Comprehensive Reach 3. Third Factor: The Inescapable and 376 Automatic Nature of the Collection 4. The Test 378 D. Applying the Carpenter Test 378 1. Very Likely Covered: Web 378 Browsing Records 2. Most Likely Covered: Massive 381 Collections of Telephone and Bank Records 3. Uncertain Application: Databases of 383 Medical Records and Genetic Information III. BEYOND THE CORE TEST OF CARPENTER 385 A. Carpenter as a Replacement for Katz 385 1. The Subjective Prong: Katz Has Only One Step 386 2. The Objective Prong: Victory of the 387 Normative Fourth Amendment 3. The Argument for Moving Beyond Katz 389 B. The Third-Party Doctrine, Inside Out 390 C. Carpenter and Direct Government Surveillance 392 D. The New Rule of Technological Equivalence 394 1. Information from Inside the Home 394 2. Bailment 396 3. Private Communications 398 IV. CARPENTER'S TECH EXCEPTIONALISM 399 A. Rejecting Conventional Analogies 400 B. The Chief Justice's Tech Exceptionalism 401 C. The Argument for Tech Exceptionalism 403 D. Expertise and Analogy 405 E. Time and Technological Change 408 F. Refusing to Look Backwards 410 1. The Surveyors 410 2. The Legal Historians 412 3. The Positive Law Proponents 413 4. Looking Forward Not Backward 413 V. CONCLUSION 415 I. INTRODUCTION

The Supreme Court's opinion in Carpenter v. United States (1) has been heralded by many as a milestone for the protection of privacy in an age of rapidly changing technology. (2) Despite this, scholars and commentators have failed to appreciate many of the important aspects of this landmark opinion. Carpenter works a series of revolutions in Fourth Amendment law, which are likely to guide the evolution of constitutional privacy in this country for a generation or more.

The most obvious revolution is the case's basic holding--formation about the location of cell phone customers held by cell phone providers is now protected by the Fourth Amendment, at least when the police seek seven days or more of such information. (3) For the first time, the Court has held that the police must secure a warrant to require a business to divulge information about its customers compiled for the business's purposes, reinventing the reasonable expectation of privacy test and significantly narrowing what is known as the third-party doctrine. (4) This cell-site location information ("CSLI") has become a key source of evidence for criminal investigations, so this holding will revolutionize the way the police build their cases, requiring a warrant where none has been required before. (5)

Building outward, the reasoning of the majority opinion, written by Chief Justice Roberts and commanding five votes, revolutionizes the law of police access to many other types of information, in addition to CSLI. (6) Databases that can be used, directly or indirectly, to ascertain the precise location of individuals over time are likely now covered by the Fourth Amendment. The police will probably need a warrant to obtain location information collected by mobile apps, fitness trackers, connected cars, and many so-called "quantified self technologies. (7)

The reasoning extends beyond location information, although predicting the scope and shape of this revolutionary step requires a bit more speculation. The majority opinion promulgates a new, multi-factor test that will likely cover other commercially significant data that the police have begun to access in its investigations. (8) Massive databases of web browsing habits stored by internet service providers (ISPs) (9) will probably now require a warrant to access. Perhaps most surprisingly, the majority's reasoning will apply even to massive databases of telephone dialing and banking records, cutting back on the holdings of two cases, Smith v. Maryland (10) and Miller v. United States, (11) that the Carpenter Court expressly declined to overrule. (12) Those two cases are in a much more precarious state than other commenters have recognized. (13)

Looking beyond the central holding and reasoning, to dicta from the majority and dissenting opinions, another class of revolutions comes into view. The Court has breathed new life into Kyllo v. United States, (14) the 2001 case that required the police to obtain a warrant to aim a thermal imaging device at a private home. (15) At least seven justices of the Carpenter Court suggest a heretofore unrecognized rule building on Kyllo: the rule of technological equivalence. If a technology, or a near-future improvement, gives police the power to gather information that is the "modern-day equivalent" of activity that has been held to be a Fourth Amendment search, the use of that technology is also a search. (16) This is a far simpler and more straightforward test to apply than the multi-factor core test of Carpenter, and for that reason, could end up becoming the Carpenter rule cited most often as the basis for requiring the police to get a warrant.

The last revolution is a revolution of legal reasoning. In his opinion, the Chief Justice evinces, as he did in the majority opinion in Riley v. California, (17) a profound tech exceptionalism. (18) Recent advances in information technology are different in kind, not merely in degree from what has come before. This idea finds substantial support in two decades of legal scholarship about threats from technology to information privacy, work that has never before received such a profound endorsement from the Supreme Court.

In embracing tech exceptionalism, the Court expressly declined invitations from scholars and amici to base its Fourth Amendment reasoning in traditional disciplines such as history or economics. (19) Scholars coming from those interdisciplinary traditions have expressed disappointment about this choice, which is an understandable reaction to having been heard and rejected. (20)

Carpenter is an inflection point in the history of the Fourth Amendment. From now on, we will be talking about what the Fourth Amendment means in pre-Carpenter and post-Carpenter terms. It will be considered as important as Olmstead (21) and Katz (22) in the overall arc of technological privacy. (23)

This article proceeds in three parts. Part II first lays out the new rule of Carpenter, which protects large databases full of information from unreasonable police access according to a new, multi-factor test, and then applies the test to private databases of information beyond the one at issue in the case. Part III explains how Carpenter has turned the government action rule of the Fourth Amendment on its head and created three new rules of technological equivalence. Finally, Part IV discusses the tech exceptionalism at the heart of Carpenter and how it changes Fourth Amendment reasoning.


    Carpenter held that the government collection of CSLI is a search by introducing a new, multi-factor test. (24) This test serves the dual purpose of deciding: (1) whether access to large databases full of personal information about individuals constitutes a search under the Fourth Amendment and (2) whether the third-party doctrine should extend to such access. (25)

    The Court did not exhaustively specify or defend the new test, although a close reading of the opinion reveals the critical factors and why they matter. (26) When the police seek to obtain information about individual behavior contained in a private party's database, the court examines (1) "the deeply revealing nature" of the information; (2) "its depth, breadth, and comprehensive reach"; and (3) "the inescapable and automatic nature of its collection." (27) The importance of these factors finds great support in recent legal scholarship. (28) When lower courts apply these factors, they are likely to extend the Fourth Amendment to cover many important commercial databases that have never before required a warrant for the police to access.

    1. Carpenter's Broad New Rule (29)

      Carpenter held that the police may not collect historical CSLI from a cell phone service provider without a warrant. (30) Footnote three restricted the holding, for now, to seven days of collection. (31)

      This is the opinion most privacy law scholars and privacy advocates have been awaiting for decades. (32) Oceans of ink have been spilled by those worried about how the dramatic expansion of technologically fueled corporate surveillance of our private lives automatically expands police surveillance too, thanks to the way the Supreme Court has construed the reasonable expectation of privacy test and the third-party doctrine. (33) The Fourth Amendment protects only that which is protected by a "reasonable expectation of privacy" ("REP"). (34) This requires a two-pronged analysis, "first that a person have exhibited an actual (subjective) expectation of privacy and, second, that the expectation be one that society is prepared to recognize as 'reasonable.'" (35) The third-party doctrine says that information a person voluntarily discloses to a third party is not protected by a reasonable expectation of privacy. (36)

      With Carpenter, the Supreme Court reinvents the REP test. Until now, the Supreme Court has tended to pay more attention to the nature of the police intrusion required to obtain information than to the nature of the information obtained. Information has been deemed protected by REP because the police obtained it using advanced thermal imaging tools, (37) or a wireless beeper located inside a house. (38) Information has fallen outside an REP when obtained from trash left on the curb, (39) low-flying aircraft, (40) or a wireless beeper traveling on public roads. (41) The analysis has almost always turned primarily on the invasion and only secondarily on the...

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