Emergency population warning

An emergency population warning or public warning system is a method whereby local, regional, or national authorities can contact or notify members of the public to warn them of an impending emergency. These warnings may be necessary for a number of reasons, including: weather emergencies such as cyclones, flooding, tornadoes, avalanches and severe weather; geological disasters such as earthquakes, landslides, volcanic eruptions, and tsunamis; industrial disasters such as the release of toxic gas or contamination of river water; radiological disasters such as a nuclear plant disaster; medical emergencies such as an outbreak of a fast-moving infectious disease or pandemic; warfare such as air raids or acts of terrorism; and other events, such as prison escapes, abducted children or emergency telephone number outages.

Source: Wikipedia — Emergency population warning (CC BY-SA 4.0)