A police siren is a loud, attention-grabbing device used by law enforcement vehicles to signal an emergency or request the right of way. It is typically accompanied by flashing lights to alert other drivers and pedestrians to make way for the police vehicle during urgent situations such as emergencies or high-speed chases.
For the purpose of early patient transport an ambulance may use as signal the wailing siren sound having rising and falling loop; while a police vehicle in emergency service will use siren with passing sound effect with short brust.