Riley v California was actually two separate cases wherein police searched data on cell phones without a search warrant. The holding is that the interests in protecting officers' safety did not justify dispensing with warrant requirement for searches of cell phone data and interest in preventing destruction of evidence did not justify dispensing with warrant requirement for searches of cell phone data.
In the opinion the court went into its standard discussion wherein the fourth amendment requires a warrant issued by a neutral and detached magistrate. In the absence of a warrant the search is reasonable only if it falls within a specific exception to the warrant requirement. Custodial arrest of a suspect based upon probable cause is a reasonable intrusion. In determining whether to exempt a given type of search from the warrant requirement, a court must assess on the one hand, the degree to which it intrudes upon an individual's privacy and on the other hand the degree to which it is needed for the promotion of legitimate governmental interests.
The government's argument that the cell search was necessary to protect officer's safety failed because the phone could not be used as a weapon to harm officers or to effectuate arrestees escape. Also, the government's argument that the search of cell data was permitted under the search incident to arrest exception failed.
Cell phones differed from other physical objects both quantitatively and qualitatively, given phones' immense storage capacity, collection in one place of many distinct types of private information, and ability to convey more information than previously possible, and phones also presented issue that they can access information not stored on phones themselves. Exceptions to the warrant rule did not cover such information.
SCOTUS went on to state that allowing police to conduct warrantless search of call logs on arrestees' cell phones was unwarranted under search incident to arrest exception to warrant requirement, since those logs would typically contain not only phone numbers, but also identifying information that arrestee might have added, such as labels for incoming calls.
Other topics the court raised as needing definition are how to limit warrants to allow only access to information sought in a warrant and what procedure is in place governing destruction of evidence discovered outside of the search warrant parameters.
This issue will most certainly be developed in year to come. As a practitioner I frequently encounter search warrants for cell phones that result in thousands of pieces of data. The typical digital analysis software used by law enforcement in this area of the country is called Cellebrite. There already have been federal courts that have addressed some of these issues.
