Public Earthquake Warning System for Japan
In 2007, Japan began operation of its nationwide public warning system that now makes use of 1100 seismic stations operated by the Japan Meteorological Agency (JMA) and the National Research Institute for Earth Science and Disaster Prevention (NIED). The JMA-operated system issues alerts via TV, radio, cell phones and a plethora of other specialty devices developed by the private sector.
For a summary of the history of the Japanese system see
Kamigaichi et al. 2009
Map showing seismic stations used by the Japanese system. From Kamigaichi et al, 2009.