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The Digital Fourth Amendment: Privacy and Policing in Our Online World
When can the government read your email or monitor your web surfing? When can the police search your phone or copy your computer files? In the United States, the answers come from the Fourth Amendment to the Constitution and its ban on 'unreasonable searches and seizures.'
The Digital Fourth Privacy and Policing in Our Online World takes the reader inside the legal world of how courts are interpreting the Fourth Amendment in the digital age. Computers, smartphones, and the Internet have transformed criminal investigations, and even a routine crime is likely to lead to digital evidence. But courts are struggling to apply old Fourth Amendment concepts to the new digital world. Mechanically applying old rules from physical investigations doesn't make sense, as it often leads to dramatic expansions of government power just based on coincidences of computer design.
Written by a prominent law professor whose scholarship has often been relied on by courts in the field, The Digital Fourth Amendment shows how judges must craft new rules for the new world of digital evidence. It explains the challenges courts confront as they translate old protections to a new technological world, bringing the reader up to date on the latest cases and rulings. Informed by legal history and the latest technology, this book gives courts a blueprint for legal change with clear rules for courts to adopt to restore our constitutional rights in the computer age.
The Digital Fourth Privacy and Policing in Our Online World takes the reader inside the legal world of how courts are interpreting the Fourth Amendment in the digital age. Computers, smartphones, and the Internet have transformed criminal investigations, and even a routine crime is likely to lead to digital evidence. But courts are struggling to apply old Fourth Amendment concepts to the new digital world. Mechanically applying old rules from physical investigations doesn't make sense, as it often leads to dramatic expansions of government power just based on coincidences of computer design.
Written by a prominent law professor whose scholarship has often been relied on by courts in the field, The Digital Fourth Amendment shows how judges must craft new rules for the new world of digital evidence. It explains the challenges courts confront as they translate old protections to a new technological world, bringing the reader up to date on the latest cases and rulings. Informed by legal history and the latest technology, this book gives courts a blueprint for legal change with clear rules for courts to adopt to restore our constitutional rights in the computer age.
- GenresLawNonfiction
264 pages, Hardcover
Published January 10, 2025
15 people are currently reading
95 people want to read
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Displaying 1 - 6 of 6 reviews
February 5, 2026
5 stars bc no wonder this man has been cited in ten million court opinions bc this is how you do legal advocacy, like these proposals were primed and ready to go. Overall a very readable distiller on 4A tech law and I enjoyed it even though there were things that frustrated me, like waffling on whether we should eliminate the border exception for noncitizens - at minimum the exception seems blatantly inapplicable to anyone who at least has legal status so it kinda confused me that he wasn’t willing to push that further. I also didn’t fully buy the plausibility of some of his other proposals (espec on use restrictions, like id rly rather err on the side of a search restriction given potential for abuse) but that’s more from my issues w the system, like if we’re accepting as a baseline that police can do things then like ok yeah okay
January 26, 2026
Very good for what it is. Orin Kerr is a really good scholar and did a nice job systematizing Carpenter. Good idea to power down your cell phone when crossing borders.
January 29, 2025
Orin Kerr brings a career’s worth of study to this broadly accessible book discussing the way the fourth amendment applies (and how it should be interpreted) when dealing with digital technologies. Kerr’s style is eminently readable - he has a great skill of making complicated topics understandable. If you are a person concerned about the ways emerging technologies increasingly used by law enforcement threaten to reduce the scope of individual privacy, this is a great read for you.
January 28, 2026
Earlier this month, the Supreme Court agreed to hear Chatrie, a case in which the Court will decide whether geofence warrants comport with the Fourth Amendment.
Orin Kerr is the country’s preeminent Fourth Amendment scholar, and so I decided to read his new book, The Digital Fourth Amendment. The book draws primarily from Kerr’s prior scholarship. It’s comprehensive, readable, and persuasive.
Kerr sets forth his basic idea in Chapter 3, “Equilibrium-Adjustment.” It goes like this:
Throughout the book, Kerr answers tough questions directly. Each piece of information looked at is a “search” for Fourth Amendment purposes. Taking an “image” (copy) of the data on a device is a “seizure.” He makes a persuasive case for why we should retain rights over copies made by the government. He draws lines between responsive & nonresponsive data and content & metadata that fit nicely with distinctions in the physical world. And Kerr comes out swinging against the border searches and the plain-view doctrine in the digital context. Laudably, Kerr acknowledges that he doesn’t have all the answers. For example, he wisely leaves open questions about the interplay between border searches and noncitizens (pp. 128–29).
In Part III (“Networks”), takes on the “misunderstood” third-party doctrine (pp. 144-47). He discusses Jones (2012) and Carpenter (2018) favorably, but he doesn’t explain how courts actually do the mechanics of equilibrium-adjustment. The mechanics of his argument are unclear. Basically, lower courts should try a bunch of things and then, after enough time has passed, the Supreme Court should pick the best “adjustment.” In his defense, Kerr concedes that Carpenter “demands line drawing where no obvious lines exist” (p. 155).
Kerr’s major proposal to decide whether to Carpenter-ize records is the “NPU test—for New, Personal, and Unavoidable” (p. 156). Only if records meet those three elements should courts engage in equilibrium-adjustment. He offers a preliminary application of this approach to a variety of modern problems, including geofencing (p. 167-68).
In the penultimate chapter, Kerr rejects the “mosaic theory” of the Fourth Amendment, which argues that “[m]uch like how many small pieces of glass can be assembled into a mosaic picture, the collection and analysis of many pieces of information about a person can produce a picture of their private lives” (p. 172). He characterizes the questions raised by this theory as “unanswerable” (p. 174), and in my view makes quick work of the theory, though he includes a caveat for the potential of AI to make it easier for the government to assemble a complete view of our private lives (pp. 185-86).
In the final chapter, Kerr characterizes the practice of governments buying data as “an important privacy problem, but … not a Fourth Amendment problem.” I’m unconvinced, and Kerr himself concedes that “[s]omeday … equilibrium-adjustment may be necessary” (p. 194).
Kerr’s book is clearly intended to be read by judges and the justices themselves. But it’s eminently readable, starting with Entick (1765) and Fourth Amendment basics and moving to the frontier of privacy and technology. Regardless of whether you agree with Kerr’s conclusions, the book is a must-read for anyone interested in how courts can and should ensure that technological advancements don’t eviscerate the Fourth Amendment’s guarantees.
Orin Kerr is the country’s preeminent Fourth Amendment scholar, and so I decided to read his new book, The Digital Fourth Amendment. The book draws primarily from Kerr’s prior scholarship. It’s comprehensive, readable, and persuasive.
Kerr sets forth his basic idea in Chapter 3, “Equilibrium-Adjustment.” It goes like this:
Search-and-seizure rules are unusually sensitive to technology. Transformative technologies frequently disrupt how old rules operate. That disruption throws Fourth Amendment law off a preexisting balance that its rules can strike. When that happens, courts should recalibrate the rules to maintain the Fourth Amendment’s role. (p. 40).He explains, descriptively, how this principle has played out over periods of technological change from automobiles to phones and beyond. His descriptive account is persuasive, but Kerr doesn’t do enough for me to justify the approach on normative grounds. He spends a few pages urging the theory’s compatibility with originalism (pp. 54-57), and I think the approach can likely be justified on originalist grounds.
Throughout the book, Kerr answers tough questions directly. Each piece of information looked at is a “search” for Fourth Amendment purposes. Taking an “image” (copy) of the data on a device is a “seizure.” He makes a persuasive case for why we should retain rights over copies made by the government. He draws lines between responsive & nonresponsive data and content & metadata that fit nicely with distinctions in the physical world. And Kerr comes out swinging against the border searches and the plain-view doctrine in the digital context. Laudably, Kerr acknowledges that he doesn’t have all the answers. For example, he wisely leaves open questions about the interplay between border searches and noncitizens (pp. 128–29).
In Part III (“Networks”), takes on the “misunderstood” third-party doctrine (pp. 144-47). He discusses Jones (2012) and Carpenter (2018) favorably, but he doesn’t explain how courts actually do the mechanics of equilibrium-adjustment. The mechanics of his argument are unclear. Basically, lower courts should try a bunch of things and then, after enough time has passed, the Supreme Court should pick the best “adjustment.” In his defense, Kerr concedes that Carpenter “demands line drawing where no obvious lines exist” (p. 155).
Kerr’s major proposal to decide whether to Carpenter-ize records is the “NPU test—for New, Personal, and Unavoidable” (p. 156). Only if records meet those three elements should courts engage in equilibrium-adjustment. He offers a preliminary application of this approach to a variety of modern problems, including geofencing (p. 167-68).
In the penultimate chapter, Kerr rejects the “mosaic theory” of the Fourth Amendment, which argues that “[m]uch like how many small pieces of glass can be assembled into a mosaic picture, the collection and analysis of many pieces of information about a person can produce a picture of their private lives” (p. 172). He characterizes the questions raised by this theory as “unanswerable” (p. 174), and in my view makes quick work of the theory, though he includes a caveat for the potential of AI to make it easier for the government to assemble a complete view of our private lives (pp. 185-86).
In the final chapter, Kerr characterizes the practice of governments buying data as “an important privacy problem, but … not a Fourth Amendment problem.” I’m unconvinced, and Kerr himself concedes that “[s]omeday … equilibrium-adjustment may be necessary” (p. 194).
Kerr’s book is clearly intended to be read by judges and the justices themselves. But it’s eminently readable, starting with Entick (1765) and Fourth Amendment basics and moving to the frontier of privacy and technology. Regardless of whether you agree with Kerr’s conclusions, the book is a must-read for anyone interested in how courts can and should ensure that technological advancements don’t eviscerate the Fourth Amendment’s guarantees.
June 29, 2025
excellent.
November 8, 2025
Law is not keeping up with technology - some of that by design to add some friction and slow down rapid radical change. But especially in our digital world the ways law interacts with technology is causing all types of interesting questions explored here.
Displaying 1 - 6 of 6 reviews