If an officer is traveling to a call at a high rate of speed, they will usually use a wail/yelp siren sound. Cops may activate their audible warning devices when they need to get the attention of people in a crowd or on the road.
Description
Specification
A civil defense siren, also known as an air-raid siren or tornado siren, is a siren used to provide an emergency population warning to the general population of approaching danger. It is sometimes sounded again to indicate the danger has passed.