Civil defense siren

Outdoor warning device used to audibly warn about incoming or ongoing danger

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 during World War II, they were later used to warn of nuclear attack and natural disasters, such as tornadoes. 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.

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