Answer as of October 18, 2026: For the October 16 earthquake warning in Japan, NTT Docomo confirmed a failure to distribute its Area Mail alerts. Contemporary reporting says KDDI (au) and SoftBank distributed the warning successfully. Rakuten Mobile's outcome could not be verified to the same standard. There is no comparable public dataset establishing four-carrier historical failure rates or the average number of seconds each takes to reach a handset. The defensible ranking is au and SoftBank tied for this incident, Docomo behind, Rakuten undetermined.[1][2]
1. The false alarm that exposed a real malfunction
On October 16 at approximately 12:40 p.m. Japan time, the Japan Meteorological Agency issued an earthquake early warning covering areas from Hokkaido to central Japan. A real magnitude 6.9 earthquake occurred near Kamchatka, but the warning calculation dramatically overestimated an earthquake in the Kuril Islands region as magnitude 9.9. The agency later withdrew the warning, explained its error, and announced urgent preventive measures.[3][4]
Some observers wondered whether Docomo had actually "won" by remaining silent during a false alarm. That is a tempting punchline but a poor safety test. Docomo said the incoming data differed partly from its usual format, which its system failed to recognize. It was an accidental delivery failure, not an intelligent decision to filter incorrect forecasts.[1]
A broken fire alarm is not a better fire alarm because the building happens not to be burning that day.
2. Fewest delivery failures: the October 16 ranking
| Position | Carrier | What was established |
|---|---|---|
| Joint first | au / KDDI | Delivery reported successful |
| Joint first | SoftBank | Delivery reported successful |
| Undetermined | Rakuten Mobile | No equivalently verified incident result |
| Behind the confirmed successes | NTT Docomo | Regional delivery failure acknowledged |
This table assesses one operator-level incident, not every customer's phone or a percentage of successful handset receptions. Docomo identified affected intended distribution regions including Hokkaido, Tohoku, Hokuriku, Kanto, Koshin, Tokai and the Izu Islands.[1][2]
3. Most failures: reverse the view carefully
For this single event, the confirmed broad distribution failures are: Docomo, one incident; KDDI and SoftBank, no failure reported for this event; Rakuten, undetermined. One incident does not mean one affected phone. Conversely, an absence of reported failures is not a proof that every device received the alert.
Docomo says its software response was completed October 17 at 7:04 p.m. Japan time. A review of the October 16 failure must therefore distinguish the incident from a claim that the same problem is still ongoing.[1]
4. What about older incidents?
SoftBank published a notice in November 2012 concerning certain phones that could sound an alarm for less than a second or fail to display a popup in specific conditions.[5] That was primarily a device-level alert presentation issue, materially different from the 2026 Docomo distribution-system failure. We could not establish a comprehensive, consistently counted history of all such incidents across Japan's four main networks.
Counting only easily searchable press releases would reward companies that publish less, which would be quite a spectacularly bad reliability metric.
5. The four-second specification is not a speed league table
An international public-warning standard calls for a primary, short emergency notification to reach in-coverage devices within four seconds measured from the operator network's receipt of the notification. Detailed secondary notifications have a different requirement; switched-off and out-of-coverage phones are excluded.[6]
That four-second target does not measure the earthquake-to-phone interval or the JMA-announcement-to-phone average. Nor is it four measured carrier results. Comparable real-world arrival-time averages for Docomo, au, SoftBank and Rakuten were not established by this research.
A fast 5G download benchmark or a low ping is not a substitute. Emergency warnings are broadcast over a system different from ordinary one-to-one messaging.[7]
6. The meaningful overall ranking
For this event only: au = SoftBank at the top, Rakuten undetermined, Docomo with the verified delivery failure.
For long-term overall reliability and speed: insufficient comparable evidence to name a winner.
A serious comparison would monitor the same warnings, regions, handset types and network conditions, then report successful delivery rates, arrival-time medians and slow-tail values, the number of users affected, and repair durations.
7. What users can actually do
Check that your phone supports Japan's emergency alerts and that alerts are enabled. Consult the JMA's carrier guidance, and remember that coverage, power and phone state can affect reception.[7] During a real warning, protecting your head and moving to a safer position matters far more than the brand ranking.
The twist: Docomo did not outsmart a mistaken forecast. The faulty alarm was exposed by a false alarm—and was reportedly repaired the next day. Discovering a weakness before it coincides with a genuine catastrophe is the only silver lining worth claiming.
References (7)
- NTT Docomo, official October 17, 2026 notice of completed correction at 19:04 JST, affected regions and cause (unrecognized partially different incoming data format) docomo.ne.jp
- ケータイ Watch, 岩井祐一郎, 16 October 2026, report identifying successful distribution by KDDI and SoftBank and failed distribution by Docomo k-tai.watch.impress.co.jp
- Japan Meteorological Agency (JMA), announcements of 16 October 2026, initial statement and follow-up on the overestimated earthquake warning: ; https://www.jma.go.jp/jma/press/2610/16c/202610161730.html ; emergency measures: https://www.jma.go.jp/jma/press/2610/16d/202610162240.html jma.go.jp
- JMA, earthquake detail for the 16 October Kamchatka-area event, magnitude 6.9 data.jma.go.jp
- SoftBank, 15 November 2012, official notice of notification sound and popup issues on certain smartphones softbank.jp
- 3GPP TS 22.268, section 5.2, public warning system requirement: primary notification within four seconds measured from receipt at the operator's network boundary until delivery to an in-coverage device; secondary notification and exclusions are separately specified: ; July 2026 ETSI catalogue: https://standards.iteh.ai/catalog/standards/etsi/fed20736-dc9d-495a-9841-8597b57cdfa4/etsi-ts-122-268-v19-3-0-2026-07 itecspec.com
- JMA, receiving earthquake early warnings on mobile phones, with links to carrier support and configuration information: ; Osaka City, explanation of area-wide emergency broadcast: https://www.city.osaka.lg.jp/kikikanrishitsu/page/0000138830.html jma.go.jp
