Given Japan's propensity for earthquakes and tsunamis, having a standardized system to alert people of the risk of danger would be a beneficial tool to prevent injury. Unfortunately, this alert system had been implemented at the carrier level, requiring carrier-specific apps. For users of unlocked phones on an MVNO, the ability to receive these notifications ranged from zero to inconsistent, dependent on the model of phone used. Now, the Telecommunications Carriers Association has announced that as of Android 8.1, these phones can receive emergency alerts.
Although the Earthquake and Tsunami Warning System (ETWS) is a 3GPP standard, only the status codes for "earthquake," "tsunami," and "earthquake and tsunami" were assigned. Carriers are free to implement their own statuses for other types of emergency alerts, the definitions for which were contained in carrier-specific apps. These statuses—including missile attacks and terrorist activity—have now been standardized among the three major Japanese carriers.
ETWS itself is an impressive standard, as sensors operated by the Japan Meteorological Agency can automatically relay that seismic activity is occurring to the mobile network, which in turn sends an alert to connected devices in "about four seconds," according to NTT Docomo's whitepaper. Secondary notifications containing detailed data about strength are transmitted shortly thereafter.