A US federal appeals court has ruled in favor of allowing police to search cell phones without the need to obtain a warrant. Following the conviction of a Abel Flores-Lopez in a drug-related charge, Lopez filed an appeal saying that police had illegally searched his cell phones without a warrant. The 7th Circuit court's Judge Richard Posner rejected the argument, ruling that minimally invasive searches of cell phones without a warrant are permissible.
When police had arrested Lopez in a methamphetamine bust, they found one cell phone on him and two more in his truck. The police then turned on those cell phones to check for their numbers in order to use the numbers to file subpoenas to the carriers for call histories. The searches did not go any deeper than to obtain the phone number of each device.
According to Posner, this type of search is allowed without a warrant. Citing another case, United States vs. Robinson, Posner explained that a "container" on someone's body at the time of arrest can be searched for relevant evidence, but acknowledged that more thorough searches would be intrusive. For instance, if a diary were found, police can check the diary to verify a suspects name, address, and other information relevant to the crime. He believes that a cell phone search for its number is similar and even less intrusive since the number can be found without having to go through all of its contents.
Posner did touch on the use of home monitoring apps such as the iCam that could turn a phone search into an intrusive home search, but that this deep of a search into a cell phone would not be permissible. However, he doesn't draw a clear line of exactly what defines intrusive for cell phone searches, leaving that debate for another time.