The following explains how the emergency earthquake alert service works.

Notifies at once an earthquake alert to regions that have a seismic intensity of 4 or higher when an earthquake with a lower-5 level seismic intensity or greater occurs

"Emergency earthquake alert" provided by the Japan Meteorological Agency *1 Notifications are sent to target areas at once.
The emergency earthquake alert provided by the Japan Meteorological Agency analyzes the data observed by a seismometer near the earthquake origin when an earthquake occurs to immediately determine the epicenter and seismic intensity (magnitude) of the earthquake. For earthquakes with a lower-5 level or greater seismic intensity, a notification is sent as soon as possible to areas (seismic intensity of 4 or higher) where strong shaking is expected.

Updates are displayed on the standby screen of handsets with the warning tone.

The emergency earthquake alert service notifies areas/regions where strong shaking is expected using a warning tone, vibration, and screen notification.