Consent is one of the specific exceptions to the general requirement that law enforcement authorities must have a valid search warrant prior to a constitutional search (where there is also a reasonable expectation of privacy). Under Tennessee law, a person has a reasonable expectation of privacy in the contents of the person's cell phone in his or her possession (an abandoned phone may be a different story). A police officer may only search the contents of the phone if there is a valid search warrant to do so or if one of the recognized exceptions to the warrant requirement is present. In the recent case of State v. Kohlmeyer, M2014-01359-CCA-R3-CD (Tenn.Crim.App. 7-7-2015), the Tennessee Court of Criminal Appeals affirmed a trial court decision that an examination of the defendant's cell phone was valid, due to the defendant having consented to it.
Traffic stops are a common kind of encounter between a police officer and a citizen. While the legality of the initial stop must be considered, there have been a number of Tennessee cases in recent years dealing with the permissible scope of an investigation following a lawful stop. Even after a lawful stop, a citizen may not be detained unreasonably. In the recent Court of Criminal Appeals case of State v. Bourrage, M2014-01194-VVA-R3-CD (Tenn.Crim.App. 5-26-2015), the Court noted that requests for driver's licenses and registration documents, as well as "inquiries concerning travel plans and vehicle ownership, computer checks, and the issuance of citations are investigative methods or activities consistent with the lawful scope of any traffic stop."