We, secty electronics GmbH Germany, and together with the German Government, Malteser International have installed 4 early earthquake warning systems in 4 different villages for 3 weeks ago in Region Kashmir/ Pakistan. In this case is the warning area of every system around 600 till 800 meters.
There was an earthquake (5.6 Magnitude Richterskale) in this area on 20th of February. All systems given alarm seconds before the destructive S-wave reach the location of the systems.
Also for a higher safety against false alarms you can connect up to 16 detectors in a net.

The advantage of the detector is that you can adjust the swelling value of sensibility of the sensor dependent of the building.

This low cost earthquake detectors are used in 12 countries at the moment.

The system has given alarm in the German School in El Salvador last year.

I think this system is also very important for the Japanese people.

The system will give only alarm if an destructive earthquake is happens.