J-Alert (Japanese: 全国瞬時警報システム, romanized: Zenkoku Shunji Keihō Shisutemu/J Ararto) is the early warning system used in Japan. J-Alert was launched in February 2007. The system is designed to quickly inform the public of threats and emergencies such as earthquakes, severe weather, and other dangers. The system was developed in the hope that early warnings would speed up evacuation times and help coordinate emergency response.
J-Alert is a satellite based system that allows authorities to quickly broadcast alerts to local media and to citizens directly via a system of nationwide loudspeakers, television, radio, email, and cell broadcasts. According to Japanese officials, it takes about one second to inform local officials, and between four and twenty seconds to relay the message to citizens. An enhanced version of the J-Alert receivers were installed by the end of March 2019. The new models can automatically process the information within two seconds, compared to the older models that can take up to twenty seconds.
All warnings, except for severe weather warnings, are broadcast in five languages: Japanese, English, Mandarin, Korean, and Portuguese (Japan has a small Chinese, Korean, and Brazilian population, as well as British, American, and other English-speaking populations). The warnings were broadcast in these languages during the 2011 Tōhoku earthquake and tsunami. The severe weather warnings are only broadcast in Japanese.
When there is a civil emergency such as a ballistic missile heading towards Japan, a special air raid siren sounds across loudspeakers and on TV and radio. When the siren starts, if it ends when the square waves hit at 329 kHz and 203 kHz, that means that a civil emergency is in effect. If the square waves reach 261 kHz and 283 kHz, that means the missile has passed.
Many prefectures and urban areas were slow in adopting the system. Upon its introduction, the Japanese government hoped to have 80% of the country equipped with the J-Alert system by 2009. However, by 2011, only 36% of the nation had been covered. Cost had been a major factor; the initial installation is estimated to be around 430 million yen, and the yearly maintenance is estimated to be around 10 million yen.
By May 2013, 99.6% of municipalities nationwide were covered.