My Android warned me of an earthquake seconds before it happened—here’s how it knew

Two seconds before the 6.9-magnitude earthquake struck roughly 60 miles from my area on September 30, my Anrdoid phone warned me to take cover. It bought our family extra time to brace ourselves before the shaking eventually rolled through the region.

Android users across Cebu and nearby provinces likewise received the same push notification that read: “Earthquake nearby. Expect light shaking.” For many, it was their first encounter with the Android Earthquake Alerts System (AEAS), and the fact that their phones somehow “knew” before the quake hit was both fascinating and bewildering.

How your phone knows before you do

Earthquakes produce two main kinds of seismic waves: primary waves (P-waves) and secondary waves (S-waves). P-waves travel faster but usually cause less damage, while S-waves are slower and stronger, responsible for most of the shaking people feel. The seconds between the arrival of these two waves is where the alert system comes into play.

Few people realize that Android devices are capable of detecting tremors through their built-in motion sensors. Modern smartphones contain a small device called an accelerometer, which measures sudden changes in movement. It is the same sensor that allows your screen to rotate or count your steps. When an earthquake’s P-waves pass through, they cause faint vibrations—too subtle for humans to notice, but easily detected by accelerometers.

According to Marc Stogaitis, Principal Software Engineer of Android, when multiple phones in the same area detect similar movement patterns at the same time, they automatically send data consisting of time, location, and motion readings to the company’s servers. The system uses these inputs to identify the epicenter and estimate the magnitude and intensity of the quake within seconds.

If the readings match the profile of a real seismic event, Google sends a warning to users expected to feel shaking next. This means the alert can sometimes arrive a few seconds before the stronger and more destructive S-waves reach your location. This crowdsourced approach allows the system to function even in countries where mobile phone coverage is far denser than seismograph networks, such as the Philippines.

When your phone decides to warn you

The AEAS issues two kinds of warning depending on the intensity of the earthquake: “Be Aware” and “Take Action”. For mild shaking, the “Be Aware” notification is issued when the estimated intensity is low. It serves as an early notice for light quakes or distant epicenters, prompting users to stay alert.

Meanwhile, if strong shaking is expected near the epicenter, the “Take Action” alert is triggered. This alert overrides your phone’s “Do Not Disturb” settings and displays a full-screen warning that provides a visual reminder to “drop, cover, and hold”. However, the alert might reach you after the shaking begins if you are too close to the epicenter, as the difference between the first and second seismic waves is almost instantaneous in nearby areas.

It is also important that users keep their mobile data or Wi-Fi enabled, since the alerts rely on an active internet connection to reach users. Residents in towns affected by power outages are therefore less likely to receive warnings in real time. I, for instance, was not notified when a more recent 5.8-magnitude earthquake struck the same area in Cebu on October 18, simply because I was asleep and had my phone’s internet connection turned off. Still, even the smallest window of preparation is better than none.

What it means for you

The Philippines sits along the Pacific Ring of Fire, making it one of the world’s most seismically active regions. In just the last two weeks, the Philippine Institute of Volcanology and Seismology (Philvocs) has recorded over 10,000 aftershocks in Bogo, Cebu and more than 1,000 in the “doublet earthquake” that hit Davao Oriental just a week after. The 5.0-magnitude earthquake in Zambales likewise jolted parts of Luzon and will continue to generate minor tremors as the crust adjusts to the initial rupture.

While no technology can truly predict earthquakes, the AEAS gives users something much more valuable: time. A few seconds to protect yourself, to take cover under a sturdy table, or to move away from falling objects. Having those advance warnings can make all the difference, especially when preparedness, not prediction, is what ultimately keeps people away from danger.