Fourth Amendment Law by Analogy

Orin Kerr is America’s leading Fourth Amendment scholar. He is brilliant, prolific, and influential, cited in numerous judicial decisions and countless law review articles. Yet despite his enormous influence and his nearly 25 years of being a law professor, he has only recently published his first book, “The Digital Fourth Amendment: Privacy and Policing in Our Online World.” His goal in doing so is to set out a big picture account of Fourth Amendment law, connecting his 40 or so prior articles on individual Fourth Amendment issues into a larger synthesis. “The Digital Fourth Amendment” presents Kerr’s overarching philosophy and allows us to see how his many excellent issue-specific analyses of Fourth Amendment questions fit together.

This review, based on a longer forthcoming review, examines the successes and failures of Kerr’s conceptual framework for Fourth Amendment law. It also offers an appreciation of the consistency of Kerr’s approach in a particular context: government officials copying digital data. There, following the principles of his broader theory of Fourth Amendment law, Kerr advocates for an aggressively protective approach to data in an area where many others (myself included) would support a less protective approach.

In “The Digital Fourth Amendment,” Kerr illuminates the major Fourth Amendment cases of the past century in an engaging, story-first way. He clarifies the issues that today’s judges are likely to face and explains them in a manner that readers with no prior knowledge of Fourth Amendment law can understand. His individual arguments are thoughtful and often compelling, and the breadth and depth of his knowledge of Fourth Amendment law is unparalleled. “The Digital Fourth Amendment” offers an excellent overview of Fourth Amendment law in the modern world. At the same time, Kerr’s heavy reliance on analogies to the physical world often leads him to under-protect online data, which today may reveal remarkably large portions of people’s lives. The further away new technologies get from traditional Fourth Amendment contexts, the less guidance and constraint the analogical approach provides.

Analogy and Adjustment

“The Digital Fourth Amendment” is divided into three parts. The first provides an excellent overview of Fourth Amendment law and Kerr’s influential scholarship on surveillance and technological change. It describes the law of searches and seizures, the meaning of “unreasonable” in the Fourth Amendment, and some of the traditional rules governing searches and seizures in the physical world. It then examines how new digital technologies and investigative practices affect this body of law.

The second part offers Kerr’s analyses of the law governing digital data on physical devices. It examines searches and seizures of computer hard drives and the data they hold. It explores the questions of how to particularize a warrant to search an entire computer hard drive for distinct digital evidence. Additionally, it looks at searches of electronic devices at the nation’s borders.

Finally, the third part of the book considers digital data on the internet, a massive category of data and the locus of many modern investigations. It discusses the differences between content and non-content data. It then addresses the Supreme Court’s transformative 2018 decision in Carpenter v. United States, which held that digital records held by cell phone companies are protected by the Fourth Amendment. It concludes by examining the government’s increasingly common practice of purchasing data from private data brokers for use by law enforcement officers.

At the center of Kerr’s approach to digital Fourth Amendment law is a reliance on analogies to the physical world. It is easy to grasp the idea that rules developed to govern police investigations in the physical world should be applied to the transformed but roughly analogous terrain of the digital world. Analogies to physical-world contexts lie at the core of Kerr’s views about most of the issues discussed in the book, from wiretapping to email, login IP addresses to the to/from data in emails and other electronic messages, to ride-sharing records, and more.

As Kerr acknowledges, analogy is often fraught with peril because of the many ways that digital information and evidence have changed modern police investigations. In many respects, the digital world is fundamentally different from the physical world. Thus, the analogies we might draw between them are often imperfect and, occasionally, actively misleading. Kerr details many ways that the collection and transmission of digital information have changed modern police investigations, and he notes that these changes can disrupt and devalue physical-world analogies. In these situations, Kerr asserts, courts can engage in “equilibrium-adjustment,” although this should occur only when the technology “has a transformative effect” on the preexisting rule.

Kerr’s combination of analogy and adjustment provides a practical framework for Fourth Amendment law, although one with relatively little theoretical bite. It becomes clear over the course of the book that equilibrium adjustment is more of an “intuitive,” practical inquiry than a normative theory of law. It’s a search for a “ballpark level of limits on police power” within the “range of the reasonable, somewhere in the middle, that most will feel permits enough enforcement of the law without giving government too much power.” In practice, the equilibrium adjustment inquiry is often a totality-of-the-circumstances-style approach, involving an intuitive judgment about whether and how much to adjust doctrines developed in analog circumstances. Nonetheless, in practice, analogy tends to play the largest role in Kerr’s theoretical approach, with adjustment reserved for truly transformative circumstances. In the absence of an overarching theory of Fourth Amendment law or its core values, analogies to the physical world can help us reach answers to otherwise difficult Fourth Amendment questions.

Yet these conclusions, grounded in physical-world contexts, are sometimes a poor fit for the circumstances of the modern digital world. Kerr’s largely analogical framework contributes to his tendency to advocate for a narrow, pro-surveillance approach to online data, especially in the book’s third and final part. In prior parts, Kerr’s uses of analogies and interest balancing are relatively straightforward. Kerr follows the logic of his approach wherever it leads, often advocating for an expansion of Fourth Amendment protections to more closely preserve the function of the old doctrines. But Kerr’s focus on the physical location of internet data and use of distant analogies to real-world settings often leads him to urge under-protecting privacy in online contexts. The result is a series of frontier Fourth Amendment questions that are nearly all answered the same way: The Fourth Amendment should not apply to online data in most controversial cases, including geofence data, login IP addresses, location and other data purchased by the government from data brokers, license plate tracking records, ride-sharing app records, and more. Taken together, this lack of protection against modern forms of surveillance would threaten to leave people with little security against pervasive government monitoring and an ever-shrinking sphere of privacy.

Fourth Amendment Data Seizures

Whatever its normative implications, Kerr’s application of his analogical principles is admirably consistent. One interesting example of this conceptual coherence is Kerr’s argument that the police “seize” data for Fourth Amendment purposes when they copy it. He contends, for example, that police seize data whenever they tell online service providers such as Facebook to preserve the data associated with a person’s account pending further police investigation. When Facebook copies the data at government request, Kerr says, it is acting as an agent of the government and seizing the data. He also argues that police copying data from a suspect’s computer after lawfully gaining access to the computer during a home search is a seizure.

Kerr acknowledges the uncertainty surrounding this issue, on which courts have largely not weighed in. The relevant precedents from the pre-internet era point in opposite directions, and none addresses digital data. Kerr ultimately resolves the question via an analogy to seizures in the physical world. Prior to the invention of computers, when police entered a home and wanted to use papers inside it as evidence, they would physically remove the papers. In the digital era, police can copy data without physically removing it. In order to preserve the old approach, Kerr argues that courts should declare the copying or preservation of data to be a seizure. After all, “copying is a way of gaining control of data in the modern world.” Declaring copying to be a seizure, Kerr says, allows data owners to remain more fully in control of their data, and “assures preservation of the limits on government control that existed before the computer age.”

This is a plausible approach to an uncertain question. I see it differently, however. Copying data does not “seize” it for Fourth Amendment purposes because it does not meaningfully interfere with a possessory interest in the data. Recording information about something may be a Fourth Amendment search in some cases, but it is not a seizure, for several reasons.

First, courts have established that the government can copy serial numbers or photograph things to which it has lawful access without seizing them, and intangible data should be treated no differently. Copying a sheet of paper is similar in practice to photographing it, and it is plain under the relevant precedents that photographing a document or anything else at a crime scene is not a seizure. Nothing about digital data should change this analysis. Data found in a computer at a crime scene can be copied without effecting a seizure just as data found on sheets of paper can be. Nor is the copy Facebook makes of a suspect’s account a seizure of that account. It is essentially a photograph of the account as it currently exists, and it does not displace or harm a user’s account any more than a photograph would harm their papers. Of course, it may be an unlawful search (or at least might facilitate a later unlawful search) for the government to direct Facebook to copy all the data associated with a suspect’s account. But merely copying or photographing something does not seize it.

Second, Kerr rests much of his argument on an analogy between copying data and seizing pamphlets from a home. But this analogy sheds little light on the seizure question because by copying the government does not take anything away. It is true that, with data, copying it is even more convenient for the government than seizing it, and physical seizure is largely irrelevant when it comes to computer hard drives and the like. But this does not mean that we must create a new and overbroad concept of seizure on the basis of a distant analogy. It means that access to data is governed by the law of Fourth Amendment searches, and seizure is generally not a useful concept in the context of intangible data.

Third, Kerr’s approach would create tricky line-drawing problems. He acknowledges in prior work that his approach compels him to distinguish cases in which police officers simply record—that is, copy—data that they observed at the scene, such as serial numbers on stereo equipment. His proposed distinction is that police can copy data that they personally observe but cannot copy data they have not yet personally observed. But this distinction makes little sense and raises some odd practical issues. Is it enough for police officers to skim documents they copy at a crime scene, or do they need to read every line? What if they read the text but do not understand it, and its meaning is revealed only later when an expert reads it? More to the point, if a police officer reads some documents on a hard drive but not others, why should copying the read documents not be a seizure under Kerr’s analogy? If copying data is truly like seizing a pamphlet, it should not matter if someone reads it before seizing it. The government is still taking control of the data under Kerr’s analysis, whether an officer looks at it first or not. In other words, copying data can either be a seizure or not a seizure; reading it is neither here nor there.

The practical policy stakes of this particular debate may be low because the police cannot lawfully access any copies that Facebook makes of the private portions of someone’s online accounts until they secure a warrant, and federal law gives them only 180 days to do so before the copy is deleted. The privacy harms of telling Facebook to make a copy of someone’s account pending further investigation are essentially nil if no one ever actually looks at the copy. And the potential privacy harms related to the storage of lawfully searched data in a hard drive are limited by the fact that the police need a search warrant to access the data in the first place.

But behind disagreements over particular questions of this sort lies a subtle, but important, difference in views about the values that animate the Fourth Amendment. Kerr’s emphasis in this context and many others in the book is on quasi-property concepts such as possession and the right to exclude others, even as he eschews actual property rights in his analysis. Throughout the book, values like informational privacy often weigh less heavily than these concepts drawn from property law. My approach, and the approach of many Fourth Amendment scholars, tends to weigh privacy more heavily.

Clarity and Integrity

Whatever our disagreements, Kerr follows the principles of his approach with admirable consistency, as in the context of data seizures. His integrity is admirable and so is the clarity and coherence of his framework for Fourth Amendment law, at least at the level of individual issues. Kerr’s ability to establish and defend clear rules for resolving tricky Fourth Amendment cases is one important reason out of many for his enormous influence on the field.

Examples of these qualities can be found throughout the book. One of the most convincing chapters discusses inspections of digital devices at U.S. borders. Traditionally, the government is allowed to physically search people and property at the border without any cause. Kerr examines the three rationales for this power—customs enforcement, immigration enforcement, and blocking contraband—and finds that all of them are tied closely to the physical nature of border crossing. He argues that none of these rationales has purchase in the new context of digital data, at least so long as the device holder is a U.S. citizen. Another compelling chapter addresses how to administer warrants for digital evidence stored in a computer or similar device. Kerr proposes a clear and administrable approach that would allow police to search the entire hard drive for evidence of the crime specified in the warrant but would forbid the government from using any incidental evidence they find of other crimes in court. He is able to fashion something like the prior, physical-world rule while also recognizing that hard drive searches differ too much from physical searches to rely entirely on prior law.

“The Digital Fourth Amendment” sets out a full account of modern Fourth Amendment law, by an unparalleled expert in the field. As a book-length overview of Fourth Amendment law—accessible, clear, and informative—it has no equal. Kerr’s arguments are deeply considered, and his proposals are often compelling. The book seeks to bring rules governing the physical world to bear on digital data. Its flaws as a framework for Fourth Amendment law going forward are likely to arise from profound differences between the physical and digital contexts, which are likely to multiply further as technology advances. The pragmatism and administrability of its ideas are appealing and worthy of consideration in every context. But a Fourth Amendment law capable of addressing the complex questions posed by modern technology requires more.