A
civil defense siren (also colloquially referred to as an
air-raid siren or
tornado siren) is a
siren used to provide
emergency population warning of approaching danger and sometimes to indicate when the danger has passed. Some (that are mostly located in small towns) are also used to call the volunteer fire department to go fight a fire. Initially designed to warn of
air raids in
World War II, they were adapted to warn of
nuclear attack and of natural destructive weather patterns such as
tornadoes. The generalized nature of the siren led to many of them being replaced with more specialized warnings, such as the
Emergency Alert System.