This article is written by a Japanese local.
While living in Japan, your smartphone functions not just as a communication device, but as a critical piece of “disaster prevention infrastructure” to protect your life. The core of this is the “Emergency Warning Broadcast System (ETWS) / Kinkyu Sokuho Mail” distributed by the Japan Meteorological Agency.
However, because this system incorporates Japan-specific specifications, there is a fatal pitfall: smartphones brought from your home country might not be able to receive it, or the settings might be turned off by default. This article explains how to react to the sudden blaring alarm and the objective device setting procedures to reliably receive these alerts.
1. Mechanics and Alarm Sound of ETWS
[Summary] ETWS is a Japanese public defense system that forces your phone to sound a unique, maximum-volume alarm seconds before strong tremors arrive, even if it is on silent mode.
The Earthquake Early Warning system detects the initial tremors (P-waves) of an earthquake and broadcasts an alert to all mobile phones in the target area before the destructive primary waves (S-waves) arrive.
What shocks foreigners the most is the “alarm sound.” Even if your device is set to silent or vibrate mode, the system overrides it, blaring a distinct, loud buzzer sound at maximum volume. This is not a device error; it is an objective specification designed to prompt the initial response of “instantly diving under a desk to protect your head.” When this sounds, act on the assumption that a violent earthquake will strike within seconds.
2. Procedure to Confirm Reception Settings by Device
[Summary] Visually confirm that the emergency alert switch is “ON” by checking “Settings > Notifications” for iPhone, or “Settings > Safety & emergency” for Android.
Smartphones purchased in Japan are generally turned “ON” by default. However, devices brought from overseas or devices that just underwent an OS update might have this setting turned off. Execute the following practical procedures immediately upon relocation.
- For iPhone (iOS): Open the “Settings” app and tap “Notifications.” Scroll to the very bottom of the screen and verify that the toggle switch for “Emergency Alerts” is green (ON).
- For Android: Open the “Settings” app, go to “Safety & emergency” > “Wireless emergency alerts,” and verify that the permission switches are turned on. (*Menu names may vary slightly depending on the manufacturer).
3. The Fatal Trap of Overseas Smartphones (SIM-Free)
[Summary] Some overseas Android devices lack compatibility with Japan’s ETWS reception standards, possessing an infrastructure flaw where the alarm will never sound.
For iPhones, regardless of which country in the world the model was purchased, it will properly receive ETWS as long as it is connected to a network in Japan.
However, among overseas Android devices brought from your home country (especially inexpensive SIM-free devices from emerging market manufacturers), some do not support the specific radio wave standard used in Japan called “Cell Broadcast.” In this case, even if you turn the setting on, the Earthquake Early Warning will physically not reach your phone. This is the biggest infrastructure risk that foreigners fall into.
4. Practical Q&A (Budget SIMs and the Language Barrier)
[Summary] You can receive alerts for free even on a budget SIM (MVNO) as long as it connects to a Japanese network. However, since messages are in Japanese, using a multilingual app alongside it is an absolute requirement.
Q. I am using a budget SIM (MVNO), not a major carrier. Will the alerts still arrive?
A. Yes, they will. ETWS works by broadcasting simultaneously to all devices within a specific area via the base station antennas of NTT Docomo, au, SoftBank, or Rakuten Mobile. Even budget SIMs rent lines from these networks, meaning the infrastructure guarantees free reception regardless of your line type or contract plan (data-only or voice included).
Q. Are the emergency alert messages displayed in English?
A. Basically, they are displayed only in “Japanese.” Even if the alarm sounds and you look at your screen, if you cannot read Kanji, you cannot objectively determine whether it is an earthquake, a tsunami, or a missile launch (J-Alert). To compensate for this system flaw, you must install multilingual disaster apps like “NERV” or “Safety tips” (explained in the previous article) to build a dual-layered defense net.
Conclusion: Build a Two-Tier Defense with the Alert System and Multilingual Apps
Japan’s Earthquake Early Warning is one of the most advanced defense systems in the world, but for foreigners, it harbors vulnerabilities: the “language barrier” and the “risk of overseas device incompatibility.” As a roadmap immediately upon relocation, thoroughly execute the objective practical procedure: first, turn on your device’s emergency alert settings, and second, install multilingual disaster apps as a mandatory backup in case the built-in system fails or you cannot read the alert.