Opinion of the Court
range of items contained on a phone, even though people would be unlikely to carry such a variety of information in physical form. In Riley's case, for example, it is implausible that he would have strolled around with video tapes, photo albums, and an address book all crammed into his pockets. But because each of those items has a pre-digital analogue, police under California's proposal would be able to search a phone for all of those items — a significant diminution of privacy.
In addition, an analogue test would launch courts on a difficult line-drawing expedition to determine which digital files are comparable to physical records. Is an e-mail equivalent to a letter? Is a voicemail equivalent to a phone message slip? It is not clear how officers could make these kinds of decisions before conducting a search, or how courts would apply the proposed rule after the fact. An analogue test would "keep defendants and judges guessing for years to come." Sykes v. United States, 564 U. S. 1, ____ (2011) (SCALIA, J., dissenting) (slip op., at 7) (discussing the Court's analogue test under the Armed Career Criminal Act).
IV
We cannot deny that our decision today will have an impact on the ability of law enforcement to combat crime. Cell phones have become important tools in facilitating coordination and communication among members of criminal enterprises, and can provide valuable incriminating information about dangerous criminals. Privacy comes at a cost.
Our holding, of course, is not that the information on a cell phone is immune from search; it is instead that a warrant is generally required before such a search, even when a cell phone is seized incident to arrest. Our cases have historically recognized that the warrant requirement is "an important working part of our machinery of gov-
