In an opinion by Judge Posner, the Seventh Circuit held on Wednesday in United States v. Flores-Lopez that police may conduct a warrantless search of a cellular phone to determine the device’s phone number when the device is found with or on an arrested suspect. Analogizing mobile phones to diaries, address books, and other receptacles of personal objects or information, the court held that where previous case law held certain types of warrantless searches to be lawful, the equivalent search and extraction of information from a cellular phone was also lawful.
Accepting this analogy at face value, however, ignores the reality that cellular phones are quite unlike diaries, address books or other containers of objects or information. First, a cellular phone acts like many, many types of traditional receptacles of information in one—a substantial proportion of phones now are message inboxes, email inboxes, contact lists, photo galleries, and much more. The sheer quantity of information carried in one place sets cellular phones apart from such non-electronic personal items. Second, a cellular phone, unlike its address book or diary counterparts, is almost always with its owner, exposing its data to greater access by law enforcement in the event of arrest and seizure of the device. And finally, it is difficult for a user to control what personal information is stored electronically on a cellular phone, especially because such devices generate and store much of their information automatically. Indeed, the piece of information at issue in Florez-Lopez was a cellular phone’s own number—a piece of data that is automatically programmed into the device and cannot be removed by a user.
With significantly greater amounts of information stored in one place, greater access to that storehouse of information, and less control over what information is generated and stored, cellular phones are quite different from traditional diaries and address books. For this reason it is a mistake to say that an invasion of privacy with cellular phones is permissible simply because an equivalent invasion would be permissible under existing law. The Seventh Circuit’s attempt to preserve existing law could very well backfire: the same rule applied to different circumstances is, in fact, different law.
Law enforcement therefore needs a principled way to limit the applications of the analogy between mobile phones and other receptacles of information. In subsequent cases, courts will need to give law enforcement such guidance to avoid violations of the Fourth Amendment’s principles through the imperfect application of old law to new circumstances.