According to North Korean missile flies over Japan, the Japanese government sends emergency alerts to mobile phones if there's a suspected nuclear attack. How can I receive such notifications while I'm in Japan?

I'm renting a SIM card (data only, but that should be sufficient to get text messages, or notifications via the internet), and a fairly modern iPhone. Ideally I'd like to get warnings in English so I know what kind of disaster it's notifying me of, in case it's warning me of something else like a tsunami.

The Wikipedia article J-Alert states that most warnings (severe weather warnings aren't) are given in Japanese, English, Mandarin, Korean, and Portuguese. However, I haven't seen any examples of J-alert text messages being given in English.

  • 1
    Not sure about Japan's system, but Thailand has a similar SMS messaging system for emergencies and it simply sends messages to every registered phone number, no need to sign up.
    – user13044
    Aug 29, 2017 at 3:58
  • @Tom In which languages? Aug 29, 2017 at 8:16
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    If everybody is running for shelter, just follow the crowds and you'll see either water or fire soon enough ;-)
    – gerrit
    Aug 29, 2017 at 8:54
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    @AndrewGrimm - To be honest I am not 100% certain, as there has not been a need to use the system in the area I live in, but my understanding is they send an SMS in Thai and basic English (ie "Tsunami warning")
    – user13044
    Aug 29, 2017 at 11:17
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    AT&T in the USA is convinced that I want to receive every AMBER Alert in the state. Sep 28, 2017 at 12:41

2 Answers 2


Per Wikipedia, it looks like the Japanese government's J-Alert system uses SMS Cell Broadcast for notifications to mobile phones:



Basically, the messages are multicast to every single mobile device within a targeted area. This means that, if you have a Japanese SIM card (or, potentially, any or no SIM card at all) and are within a targeted mobile cell, you'll receive missile alerts, even if you have not signed up for them!

The catch is that because CB is completely indiscriminate, it's likely the alerts will only be in Japanese.

  • Maybe even phones with no SIM card at all? Sep 28, 2017 at 12:14
  • @AndrewGrimm No. WIthout sim, you basically have no working connection (not because the location, but because of being refused by the base station).
    – deviantfan
    Sep 28, 2017 at 12:23
  • @deviantfan when I take the SIM card out of my mobile phone in Australia, I think it says something about "Emergency Calls Only". Sep 28, 2017 at 12:29
  • @AndrewGrimm I know that message ... but calling 112 or 911 isn't the same cell broadcast. ... Still, while I said no before, I'm currently not that sure anymore (if CB is allowed to ignore encryption/authentication used for most parts of GSM - then it's at least possible. If bs and client implementation allow it is another question.)
    – deviantfan
    Sep 28, 2017 at 12:37
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    @deviantfan If the cell broadcast is marked as an emergency, it will be delivered even to phones without a SIM. (Phones without SIMs are still talking to base stations, they're just not permitted to do most operations.) Sep 28, 2017 at 12:57

Many countries have a service where you can register as a citizen who is currently overseas, and they will notify you about events that happen relevant to the part of the world you're currently in. For example:

I imagine the time taken to actually notify you of urgent events varies widely by country.

  • 1
    A warning coming from the USA state department regarding a missile launched from NK at Japan would arrive after the missile hit its target.
    – user13044
    Aug 29, 2017 at 3:55
  • @Tom Why would it arrive so late?
    – gerrit
    Aug 29, 2017 at 8:53
  • @gerrit Japan is only minutes away from North Korea by ICBM. Aug 29, 2017 at 11:11
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    @Tom I would expect that the US knows about a NK missile launch at the same time or even before Japan knows.
    – gerrit
    Aug 29, 2017 at 11:50
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    @gerrit - Perhaps they both know at near the same time, but US bureaucracy is slow. I have been through a few events (coup d'etat & massive riots) in foreign countries and the STEP messages came well after events have occurred. There were no STEP messages in advance of the Boxing Day tsunami in SE Asia, even though the US tsunami centers knew one was possible. I think the only benefit to STEP and other foreign registration systems is that your government knows you are there if things really go south and citizens need to be evacuated. They are not a reliable early warning system.
    – user13044
    Aug 30, 2017 at 1:02

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