Penetration of a warning signal into the world
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 sounded again to indicate the danger has passed. Some sirens especially within small towns are also used to call the volunteer fire department when needed. The generalized nature of the siren 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.