Did you know that your smartphone can detect earthquakes without the need for any additional app? Essentially, smartphone have electronic components for detecting motion. However, the practical application is limited because you will have to keep the phone perfectly still. If are really concerned about earthquakes or live in an earthquake-prone zone it is better to invest in a dedicated earthquake alarm.
Back to the smartphone, to use the phone’s inbuilt seismometer, you don’t have to install any additional apps. The built-in browser and access to the Internet will suffice.
All you have to do is keep the smartphone perfectly still on a flat surface and open http://ctrlq.org/earthquakes/seismograph.html. You will see a continuously moving waveform. If you shake the phone slightly, you will see variation in the waveform. It is very sensitive and you will be able to see even minor disturbances.