Sobriety checkpoints have been held to be an exception to the rule that law enforcement officers need probable cause to stop and, even if brief, detain a motorist in order for the detention to be constitutional. Normally, police obtain that probable cause through witnessing a traffic violation, witnessing driving which would indicate drunk driving, or receiving an anonymous tip that a person may be driving drunk. Only then can law enforcement stop and detain a person. Although officers at sobriety checkpoints do not have the probable cause usually required to stop a motorist, both the United States Supreme Court and the California Supreme Court have held that checkpoints are constitutional. In Michigan Department of State Police v. Sitz, the United States Supreme Court held that the state’s interest in preventing drunk driving was a “substantial government interest.” It further held that this government interest outweighed motorists’ interests against unreasonable searches and seizures when considering the brevity and nature of the stop.