[JURIST] The US Court of Appeals for the Seventh Circuit [official website] ruled [opinion, PDF] Wednesday that a warrantless search of a suspect’s cell phone to collect its phone number does not constitute a violation of Fourth Amendment [Cornell LII backgrounder] protections against unreasonable search and seizure. A three-judge panel unanimously rejected the defendant’s challenge to the prosecution’s use of evidence obtained through cell phone numbers collected by police at the arrest scene. Although each phone’s number was later used to subpoena months of phone records, the court held the collection of the numbers constituted a permissible search, likening a cell phone to a diary:

If police are entitled to open a pocket diary to copy the owner’s address, they should be entitled to turn on a cell phone to learn its number … [W]hat happened in this case was similar but even less intrusive, since a cell phone’s phone number can be found without searching the phone’s contents, unless the phone is password-protected—and on some cell phones even if it is.

The court declined to rule on the applicability of other warrant exceptions that exist for exigent circumstances, such as officer safety and preservation of evidence. The defendant in the case was convicted on drug charges and sentenced to 10 years in prison.

Courts have had difficulty in applying Fourth Amendment protections to modern technology. In January the US Supreme Court [official website] ruled that the government’s attachment of a global positioning system (GPS) [JURIST news archive] device to a vehicle, and its use of that device to monitor the vehicle’s movements, constitutes a search [JURIST report] under the Fourth Amendment. Last year the Supreme Court of California [official website] ruled that incident to a custodial arrest law enforcement officers may legally search text messages [JURIST report] on a suspect’s cell phone without a warrant. The court held a search of the defendant’s cell phone text messages in the police station 90 minutes after the arrest did not violate the Fourth Amendment. The California decision represents a split from the US Court of Appeals for the Third Circuit [official website] 2010 ruling and a 2009 decision [JURST reports] by the Ohio Supreme Court [official website] that both held that police must obtain a warrant before searching data stored on a cell phone. In June 2010, the US Supreme Court ruled [JURIST report] unanimously that an employer’s search of private text messages on a work-issued device does not violate the Fourth Amendment if the search is motivated by a legitimate work-related purpose and is not excessive in scope.