Emergency population warning

An emergency population warning is a method whereby local, regional, or national authorities can contact members of the public en masse to warn them of an impending emergency. These warnings may be necessary for a number of reasons, including:
Many local areas use emergency population warnings to advise of prison escapes, abducted children, emergency telephone number outages, and other events.
Requirements.
In order to develop an effective emergency warning system, certain things are required:
United Nations program.
Early warning system is the term that the International Early Warning Programme coordinated by the United Nations uses for all systems that are used to send emergency population warnings. 
The United Nations Development Programme uses the Send Word Now Emergency Notification System to alert its worldwide staff when an urgent situation arises.
Methods by country.
Australia.
The Standard Emergency Warning Signal was originally adopted by the Bureau of Meteorology in the 1970s for tropical cyclone warnings. It became a standard national emergency warning signal in 1995. It can be broadcast on radio, television, automated telephone calls and in some places by public address systems in the event of bushfire, flood, cyclone, tsunami, earthquake or terrorist attack.
Canada.
On June 11, 2009, the Canadian Radio-television and Telecommunications Commission (CRTC) approved a proposal by Pelmorex, owners of The Weather Network and MétéoMédia, to receive must-carry status for the channels, in exchange for developing a "national aggregator and distributor" of localized emergency alert messages compliant with the Common Alerting Protocol. The alert system, known as Alert Ready, built on a backend known as the National Alert Aggregation and Dissemination system (NAAD), was first established in 2010, and further expanded as a result of consultation with government officials, broadcasters, and the CRTC. In August 2014, the CRTC ruled that all television stations, radio stations, and broadcast distribution undertakings had to begin mandatory carriage of local alerts relayed through NAAD by March 31, 2015.
The province of Alberta had its own system called the Emergency Public Warning System (EPWS). The EPWS was put into place after a major tornado swept through the city of Edmonton in 1987, killing 27 and causing millions of dollars in damage. Unlike the American EAS, however, broadcast of the EPWS was not mandatory on radio and television stations. It was broadcast on the CKUA Radio Network and was televised on CTV Two Alberta and other participating stations. EPWS warnings could be initiated by municipal police and fire departments, the provincial government, county authorities, tribal government agencies, Environment Canada, and the Royal Canadian Mounted Police. CKUA developed and maintained the EPWS until January 2010, when it lost a bid to modernize the system to an outside vendor (the contract had provided 15% of the station's overall budget). 
In June 2011, an updated version of the system known as Alberta Emergency Alert was introduced, which emphasized multi-platform availability of alerts and advisories on digital platforms, such as online and through a mobile app. Participation in AEA is now considered mandatory under the CRTC's national public alerting mandate.
France.
In France, the population warning is made via air raid siren. This network is called the "Réseau national d'alerte" (RNA). The system is inherited from the air-raid siren network ("défense passive") developed before World War II. It consists of about 4,500 electronic or electromechanical sirens placed all over France.
In some cases, the warning signal may be played by a mobile system installed on the fire department's vehicles.
The warning signal is described by "décret" (by law) of March 23, 2007. It consists in a modulated sound going up and down (up to 380 Hz) during the first minute, and repeated three times. The end of alert is a continuous signal lasting 30 seconds.
The system is tested every month, the first Wednesday at 11.45 in the north, 12.00 in the center, and at 12.15 in the south; for tests, the modulated signal is played only once.
When the warning signal sounds, people are expected to remain at home or the building they are in and listen to further instructions on radio via France Info, France Inter, or local stations.
Instructions may also be announced by police or fire department vehicles.
Japan.
The J-Alert system launched in 2007 aims to allow government officials to address the population directly via loudspeakers. It aims to cover earthquake, tsunami, volcano, and military emergencies.
The Earthquake Early Warning system is operated by the Japan Meteorological Agency. It is capable of delivering warnings a few seconds before S-waves can propagate to distant locations. Warnings are broadcast by radio and television stations, and compatible equipment can automatically turn on when receiving a message. EEW capability is also required for all domestic cell phones sold after 2007.
JMA also issues advisories regarding tropical cyclones in the western Pacific Ocean.
South America.
Many countries in South America have a mechanism called "cadena nacional" (). It enables the leader of the country to address the people simultaneously on all TV channels and radio stations, interrupting normal programming. In some countries, such as Argentina and Venezuela, the broadcast of these messages is obligatory. Many of these systems were created by past military governments, and political use of the mechanism is common.
Chile.
The SAE (Spanish: Sistema de Alerta de Emergencia; English: Emergency Alert System) was created as a response to the 2010 Chilean Earthquake after the failure by the national authorities to provide safety precautions and speedy information during the aftermath of the disaster. Since its inception in 2012 and through its official implementation in 2017 onwards, it has been used to provide alerts and information regarding natural disasters such as floods, wildfires, tsunami and earthquake warnings. All cell phones on sale in the country are required by law to be compatible with the SAE system since 2017. 
United States.
The bulk of emergency warnings in the United States are sent through the Emergency Alert System, implemented in 1997. The EAS can be activated by national, state, regional, or local authorities, including police, fire, weather, and other governmental authorities. EAS is often activated when an unpredicted emergency such as a tornado, earthquake, or release of toxic gas happens. The vast majority of EAS alerts are generated by the National Weather Service.
The Integrated Public Alert and Warning System (IPAWS) program of the U.S. Federal Emergency Management Agency is an attempt to integrate multiple public warning technologies into a coordinated nationwide "system of systems" using the Common Alerting Protocol. Systems targeted for inclusion in IPAWS include the Emergency Alert System, the Commercial Mobile Alert System using cellular telephones and other wireless devices and the NOAA Weather Radio network.
Many states use existing air raid sirens to warn of tornadoes and flash floods. People living near certain nuclear facilities such as the Hanford Site in Washington have special radios in their home that are set to broadcast a warning signal in the event of a radiological emergency. Some emergencies (AMBER Alerts, for instance) are also sent out via e-mail, cellphone text message, and highway signs. Many U.S. institutions of higher education now use multiple warning technologies on their campuses, including outdoor and indoor sirens, public address systems, email and cell phone text messaging, and digital displays.
Prior to the adoption of the Emergency Alert System, the US used CONELRAD from 1951-1963 and the Emergency Broadcast System from 1963-1997.