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Diagram of the J-Alert system

J-Alert (全国瞬時警報システム, Zenkoku Shunji Keihō Shisutemu) is a nationwide warning system in Japan launched in February 2007.[1] It is designed to quickly inform the public of various threats. The system was developed in the hope that early warnings would speed up evacuation times and help coordinate emergency response.[2]


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.[3] According to Japanese officials, it takes about 1 second to inform local officials, and between 4 and 20 seconds to relay the message to citizens. An enhanced version of the J-Alert receivers is expected to be installed by the end of March 2019[needs update]. The new models can automatically process the information within 2 seconds, compared to the older models that can take up to 20 seconds.[4]

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). The warnings were broadcast in these languages during the 2011 Tōhoku earthquake and tsunami.[5] The severe weather warnings are only broadcast in Japanese.

For NHK and other TV broadcasters, during emergencies, the system utilizes ISDB with 1seg to automatically turn on all radios and televisions with 1seg technology and tunes to NHK for the areas at risk.

J-Alert broadcasts via both ground systems and the Superbird-B2 communication satellite.[3]

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.[6]

Information transmission capabilities[edit]

Alert messages sent on 29 August 2017 North Korean missile launch over Japan
  • Earthquake
    • Earthquake Early Warning
    • Quick updates on hypocenter, magnitude, and precautions of possible tsunami
    • Information of hypocenter, magnitude, intensities of various areas, and the presence of tsunami
    • Earthquake prediction warning for the Tōkai earthquakes
    • Earthquake prediction advisory information of the Tōkai earthquakes
    • Earthquake prediction information of the Tokai earthquakes
  • Tsunami
  • Volcano eruption
    • Emergency warning of volcanic eruption and the possibility of eruption
    • Warning of volcanic eruption and the possibility of eruption
    • Volcanic crater forecast
  • Severe weather
    • Emergency warnings for heavy rain, heavy snow, gale, snowstorm, waves, and storm surge
    • Warnings for heavy rain, heavy snow, gale, snowstorm, waves, and storm surge
    • Weather advisory
    • Information of the risk of landslides
    • Advisory information for tornado
    • Information of violent heavy rain
    • Flood forecast
  • Special emergency threats

Adoption rate[edit]

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.[2] 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.[7]

See also[edit]


  1. ^ "J-Alert: disaster warning technology in Japan – Centre for Public Impact". CentreForPublicImpact.org. Retrieved 29 August 2017.
  2. ^ a b "Japan Launches Alert System For Tsunamis And Missiles". Retrieved 29 August 2017.
  3. ^ a b c "Jアラートの概要" (PDF). Retrieved 29 August 2017.
  4. ^ "Disaster agency urges municipalities to upgrade J-Alert receivers". The Japan Times Online. 7 August 2017. Retrieved 29 August 2017.
  5. ^ Tsunami Warning in multiple languages.
  6. ^ https://www.youtube.com/watch?v=IpuyQbJo9Zw. Missing or empty |title= (help)
  7. ^ Torres, Ida (31 October 2013). "J-alert to serve as early warning system during weather emergencies". The Japan Daily Press. Retrieved 29 August 2017.

External links[edit]