Civil defense siren

TWS 295 Sirens, HSS Engineering siren Warning System
Federal Signal Thunderbolt 1003
There are 8,200 alarm sirens for civil protection throughout Switzerland. They are tested once a year on the first Wednesday in February.[1] Sound sampleⓘ

A civil defense siren is a siren used to provide an emergency population warning to the general population of approaching danger. Initially designed to warn city dwellers of air raids (air-raid sirens) during World War II, they were later used to warn of nuclear attack and natural disasters, such as tornadoes (tornado sirens). The generalized nature of sirens led to many of them being replaced with more specific warnings, such as the broadcast-based Emergency Alert System and the Cell Broadcast-based Wireless Emergency Alerts and EU-Alert mobile technologies.

By use of varying tones or binary patterns of sound, different alert conditions can be called. Electronic sirens can transmit voice announcements in addition to alert tone signals. Siren systems may be electronically controlled and integrated into other warning systems.

  1. ^ Testing sirens Archived 22 October 2013 at the Wayback Machine, Swiss Federal Office for Civil Protection (page visited on 7 September 2013).