The Court of Appeals for the Seventh Circuit ruled this week on the constitutionality of whether police can conduct a "search" of a cellphone without a warrant in order to get its phone number.

The government agents had set up a sort of sting operation, which involved arresting defendants during a methamphetamine deal. In the course of the arrest, one of the defendants admitted that a cellphone found on his person was indeed his. The government then seized the phone in order to ascertain its phone number, and later subpoena the records for the number from the phone company. The government then sought to introduce these phone records into evidence in the trial against the defendant and his co-conspirators. Defendant's counsel challenged the phone records as inadmissible according to the fruit of the poisonous tree doctrine. Namely, because the initial search was unwarranted, and thus inadmissible as evidence, the records obtained pursuant to that search are also inadmissible. The district court ruled for the government, and the defendants appealed.

In the opinion, authored by Judge Posner, the court details the capabilities of today's smart phones, an discusses how phones are similar to diaries. Diaries, it discusses, are somewhat like containers, and containers are searchable, police can open them to discover what's inside. The opinion reads

And since a container found on the person of someone who is arrested may be searched as an incident to the arrest even if the arresting officers don’t suspect that the container holds a weapon or contraband, and thus without any justification specific to that container, United States v. Robinson, 414 U.S. 218, 236 (1973), the government urges that a cell phone seized as  an incident to an arrest can likewise be freely searched.

Without explicitly stating that it agrees with this position, the outcome of the opinion essentially encompasses this reasoning.

The court also discusses the fact that the Fourth Amendment does not require warrants for all searches, but rather

requires of searches without a warrant only that they be reasonable , the authority to search a person incident to an arrest , without a warrant, requires justification. The usual justification offered is “the need [of the arresting officers] to disarm and to discover evidence,” United States v. Robinson, supra, 414 U.S. at 235, or, more exactingly, evidence that the defendant or his accomplices might destroy.

Thus, searching a person without a warrant is not completely proscribed, but it is subject to standards of reasonableness, such as pursuant to preserving evidence that might otherwise be destroyed or otherwise discarded. Additionally, the opinion specifically discusses an application that can be installed in an iPhone that allows for instant access to a webcam view inside the owner's home. Viewing this application, for example, would probably cross the line into the unconstitutional, since it would rise to the level of a search of the person's home without a warrant.

The court also discusses the need to instantly get the number from a phone during an arrest because of the potential risk of remote wiping, which can remove data, meaning that by the time a warrant is executed, the phone number may no longer be there to find. Thus, in order to preserve evidence that may be destroyed remotely, the police can access a phone in order to secure its phone number.

While it broaches the topic in the beginning of the opinion, the court does not directly address the question of whether or not laptops or computer tablets may be searched. If the opinion is carried to its literal conclusion, then anything the police find in your possession may be searched, at least cursorily, in order to determine identifying information.