In a 6-3 decision in Rodriguez v. United States the Supreme Court held that a dog sniff conducted after a completed traffic stop violates the Fourth Amendment.
Officer Struble pulled over Dennys Rodriguez after he veered onto the shoulder of the highway and jerked back on the road. Officer Struble ran a records check on Rodriguez, then questioned his passenger and ran a records check on the passenger and called for backup, and next wrote Rodriguez a warning ticket. Seven or eight minutes passed between Officer Struble issuing the warning, back up arriving, and Officer Struble’s drug-sniffing dog alerting for drugs. Rodriguez argued that prolonging the completed traffic stop without reasonable suspicion in order to conduct the dog sniff violated the Fourth Amendment.