How Android phones detect earthquakes
The Android Earthquake Alerts system uses the accelerometers built into millions of smartphones to detect the first seismic waves generated by an earthquake.
Known as primary, or P-waves, these travel faster than the stronger secondary (S) waves that typically cause the most noticeable shaking and damage.
This data is automatically anonymised and reported in the background to Google, and once there are enough matching reports, an alert gets pinged out to all Android users who might be affected.
Depending on the estimated strength of the earthquake, users receive one of two alerts. A 'Be Aware' notification is sent for earthquakes below magnitude 4.5, while larger events trigger a louder 'Take Action' alert designed to grab people's attention, even if their phone is on silent.
The system is not an earthquake predictor, but rather rapidly detects an earthquake after it begins and uses the difference in speed between the initial P-waves and the slower, more destructive shaking to provide advance warning to people further from the epicentre.
The technology is now available in more than 90 countries, although its effectiveness depends on how many Android devices are nearby.
People closest to an earthquake may receive little or no warning because the shaking reaches them almost immediately, while those further away can receive several seconds' notice.
It can also be less accurate in sparsely populated areas or for earthquakes that occur offshore, where there are fewer phones available to detect the initial shaking.
https://www.1news.co.nz/2026/07/25/why-phones-woke-thousands-before-59-magnitude-taumarunui-earthquake/