1) The greatest difference a warrant requirement would impose is requiring probable cause to believe evidence will be found inside the phone. Although an arrest requires probable cause, probable cause to search is different from probable cause to arrest. Probable cause to arrest is probable cause to believe the arrestee committed a crime, while probable cause to search requires probable cause to believe evidence, contraband, fruits of crime, or instrumentalities of crime are stored in the place to be searched. The two are quite different, and often you’ll have one without the other. To see this, imagine a person is arrested for driving without a seat belt or willfully refusing to pay his income taxes. The probable cause to arrest the person doesn’t also create probable cause to believe that evidence of the seat belt violation or failure to pay income taxes can be found in any particular place. So the main role of a warrant requirement for a cell phone search case is to ensure probable cause that evidence will be found inside the actual phone.
2) In theory, the particularity requirement acts as another limitation imposed by warrants. But it doesn’t do much in this context. First, the particularity requirement imposes no limitation on the “place to be searched.” When a computer/cellphone is in law enforcement custody, the government can just list the place to be searched as the phone itself. And courts have allowed quite broad descriptions of the evidence to be seized (see p110-15). The government can’t get a warrant for “all records” in a computer, but broad categories such as “all records of gang-related activity” or “all records relating to violations of 21 U.S.C. 844” have been upheld. To find that information, the government must conduct at least a cursory look at everything in the phone. So the particularity requirement doesn’t do much in this context; it’s the probable cause finding, not particularity, that matters. (I think the limited role of particularity for computer searches provides a good reason to end the plain view exception for digital searches pursuant to warrants, but that’s probably another case.)
3) Beyond probable cause and particularity, the differences between a warrantless and warrant search for digital evidence is hard to say because the rules for computer warrants themselves are in flux. Consider this exchange from the oral argument about the role of warrants:
MR FISHER. The beauty of a search warrant is it can delineate retention rules. It can say here’s here’s how long you’re allowed to keep the information, here’s who’s allowed to look at it and who’s not. And it can –
JUSTICE SOTOMAYOR: Frankly, I have to tell you, I don’t ever remember a prosecutor coming to me with that kind of delineation.
MR. FISHER: Well, I think that, Justice Sotomayor, that is what is starting to now happen in the digital world, because we just have new and different concerns that had arisen — than had arisen in the past.
The issue resurfaced later in this exchange:
JUSTICE KAGAN: . . the whole idea of a warrant is that a neutral magistrate tells you that you can look at those things and has an opportunity to limit it in whatever way the neutral magistrate feels is
appropriate … and that’s a protection.
MR. DREEBEN: I’m not sure that I would go so far as to say the neutral magistrate can narrow the warrant in any way that he sees appropriate. This Court’s decisions in Grubbs and Dalia say that it’s not appropriate for the magistrate to prescribe the manner of executing the search.
As regular readers know, this is the debate over ex ante regulation of computer search and seizure. Some magistrates impose such restrictions; I don’t think they have any authority to do so; and only the Vermont Supreme Court has expressly weighed in on whether such restrictions are legally authorized. Right now, the answers are just uncertain.
4) Finally, there was some discussion of whether a warrant requirement would impose limitations by way of the return on the warrant and allowing ways to seek the return of seized property. I’ll just point out that, at the federal level, Rule 41 was amended in 2009 to try to answer at least some of these questions for computer searches and seizures. The provisions are modest, but it’s at least one more place to look (albeit only a statutory rule for federal searches rather than a constitutional limit on all searches).