The Idea of My New Book, The Digital Fourth Amendment—and Why It Matters

I posted yesterday about why I wrote my new book, The Digital Fourth Amendment. In this post, I want to give an overview of the book.  What’s the subject, and what’s the argument?

Welcome to 2025. If the government is trying to solve a criminal case these days, they’ll often look for digital records. Sometimes those records are collected from a suspect’s physical devices like their cell phones. Sometimes those records are collected from network providers such as Google or Meta. In both settings, the way computers work changes what evidence exists and how the government can find it.  It often means that there’s a lot of evidence out there if the government knows where to look.

So for example, in a murder case, in which the government suspects that the defendant killed his best friend for money, the government might get a warrant to search his cell phone and find stored Google searches including “are you capable of killing your best friend?” and “how does it feel when you kill someone for the first time?”  (This happened in a DC case, United States v. Burns.)  In a burglary case, in which the suspect was thought to have entered a woman’s apartment at night and illuminated his way with his cell phone flashlight, the government might get a warrant to show that the flashlight app’s log showed that it was “on” at the time of the burglary. (A Pennsylvania case, Commonwealth v. Ani.)  And if the government has a hunch that you committed a crime, investigators might tell your Internet provider to run off a copy of your entire account to store it for the government so you can’t practically delete your files.  (This happens all the time, so-called Internet preservation.)  These are just a few examples.

The big legal question is, what are the legal rules for collecting all of this digital evidence?

Enter the Fourth Amendment. The Fourth Amendment was enacted in 1791 to prohibit unreasonable searches and seizures.  It’s the primary bulwark of privacy protection against government evidence collection.  But what is a “search” of digital evidence?  What is a”seizure” of digital evidence?  And when is such a search or seizure “reasonable”?  Courts are just now trying to answer these questions.  And the answers they come to are important, as they determine what powers the government has to collect your digital evidence. And if you think that matters today, think of how important the digital rules will be in 25 or 50 years.  The future of government power hinges in no small part on these answers.

And here’s the thing: Figuring out the answers is hard!  It’s hard for a fundamental reason.  Rules about government investigations often depend on the facts.  Like all rules, they reflect the facts that exist when the rule is created.  But technological change tends to destabilize investigative rules.  A rule created in one era that had one meaning with the technological facts that existed in that era will have a very different meaning with the technological facts that exist in a later era.

This poses a basic puzzle for courts in the later era: Do you preserve the rule or the role?  That is, do you stick with the old formal legal rule, and just accept that it now has all sorts of unintended consequences inconsistent with the broader purposes and goals of the law?  Or do you try to preserve the role of the law, maintaining it over time, to make sure that the law’s protections don’t get outdated?

My book argues that courts should preserve the role, not the rule—and it then shows what new specific rules should follow from that.  Because of the way computers happen to work, sticking with the old rules would mean gutting Fourth Amendment protection over time.  And so the courts should try to retain the role of the Fourth Amendment in the new digital space—something I have called “equilibrium adjustment.”  This should lead to a set of digital specific rules for Fourth Amendment law: What I call, as the title suggests, The Digital Fourth Amendment.

Fortunately, the Supreme Court started us on this path in Riley v. California (2014) (the search incident to arrest case) and Carpenter v. United States (2018) (the cell site location records case).  Both cases echoed this answer.  After Riley and Carpenter, preserving the role of the Fourth Amendment in the digital context is not just a theory, but the Supreme Court’s directive.

But it’s one thing to have a general direction, and quite another to figure out how to get there.  Riley and Carpenter are a start, but lower courts (and eventually the Supreme Court) have to answer a ton of new questions.  For example, what is a “search” of an electronic device?  What is a “seizure” of data?  How should digital warrants be drafted?  How broad a search should be permitted?  How should exceptions to the warrant requirement like the border search exception apply, if at all? And the questions are not just about physical devices.  They’re also about the network setting.  What is a “search” in the network context?  How should courts interpret Carpenter?  Should governments be allowed to buy data outside the Fourth Amendment?

Lower courts and state courts are just starting to grapple with these questions, and much of the book is about approaches they are trying out—and my arguments for what I think they should be doing, as they try to craft The Digital Fourth Amendment.

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