The main problem with answering the question “always,” I think, is that the nature of digital evidence searches is profoundly different from the nature of physical evidence searches in ways relevant to the rationale of the search incident to arrest exception. (For this argument, I’m relying on my prior work here, here, here, and here). Unlike physical searches, digital searches cannot recover guns or knives. And the scale of digital searches is dramatically different from the scale of physical searches. In a physical world, a complete search of property a person is carrying incident to arrest is inherently a narrow search. In that setting, it was reasonable to have a bright-line rule that a complete search is always permitted incident to arrest. But when you add in digital storage devices, a complete search of property a person is carrying suddenly becomes extraordinarily broad. That scale impacts reasonableness, as the technological change renders the search orders of magnitude more invasive than it was before the digital era.

In short, I see the problem as one of equilibirum-adjustment. The new technological facts give the government dramatically expanded power under the old Fourth Amendment rule. To allow a complete search of the phone in every case — a complete forensic search through the entire computer — would give the government a tremendous power to invade a person’s privacy. In my view, that justifies a new Fourth Amendment rule to account for technological change that helps restore the prior balance of power. The point isn’t that “cell phones” should get a new rule. Today’s cell phones are really just personal computers that happen to be small enough to carry around. The real issue is digital evidence vs. physical evidence, not cell phones vs. other property.

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To reach this result, I think the Court should recognize that Fourth Amendment jurisprudence should in some cases adopt computer-specific rules. That is, the rules for searching a computer will in some cases diverge from the rule for searching physical property in otherwise analogous circumstances. This is entirely appropriate, I think, as the caselaw about automobile stops and searches has recognized. As I wrote last year:

[T]echnology-specific rules can be appropriate when technologies create recurring facts. Within Fourth Amendment law, the automobile provides the obvious example. A large chunk of Fourth Amendment doctrine concerns automobile-specific rules. Examples include the automobile exception to the warrant requirement, rules on when automobiles can be stopped, when passengers can be ordered out of the car, and when cars can be searched incident to a driver’s arrest. The computer will be to the 21st century Fourth Amendment what the automobile was to the 20th century Fourth Amendment. In both cases, transformative technologies justify technology-specific rules.

I suspect that some readers will find the idea of treating digital evidence and physical evidence differently to be counterintuitive. But I think that instinct is time-dependent:

[W]hether technology-specific rules appear natural or awkward depends on when along the technology timeline you look. In the 1990s, a computer-specific rule would have seemed exceedingly strange. At that time, encountering an electronic device during an arrest probably meant discovering a drug dealer’s pager that only stored five telephone numbers. The analogy between physical and digital devices was obvious, and a court could apply the traditional doctrine to an electronic device quite naturally. Twenty years later, that analogy is much harder to draw. But what is a hard issue today will become easy in time. Imagine how computer technologies will work in five, 10, or 50 years. Over time, advancing technology will cause the digital to seem more and more different from the physical. The need for different rules governing digital devices eventually will seem obvious.