The Japan Meteorological Association has provided some information in English on the launch of their new Earthquake Early Warning System next month. These alerts will be broadcast on TV and radio. The association concedes that there will be some false alarms and also points out one of the limitations of the new system:
"The window of time from the announcement of an Earthquake Early Warning until the arrival of the main tremors is very short, i.e. a matter of seconds (or between several seconds and a few tens of seconds). In areas that are close to the focus of the earthquake, the warning may not be transmitted before strong tremors hit."
Good luck.