Jose Flores was on his way with his family to see Toy Story 5 in Caracas, Venezuela on Wednesday when his wife’s Google Android phone sounded a loud earthquake alert. Six seconds later, he felt the ground begin to shake.
Venezuela does not have its own national early warning system, but people with Android phones received alerts from Google’s earthquake alert system, which can collect data from more than two billion phones equipped with built-in accelerometers. The same sensor that detects rotation on the screen can also sense vibrations from seismic waves.
Three seconds after the earthquake started underground
Seismic waves reached the surface and were picked up by telephones.
Google said the system, which is available in nearly 100 countries, sent alerts that reached 11.4 million people on Wednesday, giving users seconds or up to two minutes before powerful earthquakes strike.
Several countries including Japan, Mexico, Canada, etc USAthere is government early warning systems. They rely heavily on widespread regional networks of underground sensors that detect earthquakes and can send alerts to most phones—iPhone or Android—through government alert settings, which are often turned on by default.
When earthquakes occur, they send out two types of waves that travel at different speeds. Faster and softer primary waves, or P waves, travel at four miles per second and are less likely to cause destruction. The slower and stronger secondary waves, or S-waves, travel at about half the speed and cause tremors.
As P-waves begin to radiate from the epicenter, Android phones sense the vibrations, begin collecting data, and send it back to Google’s servers for processing. The servers use information from many phones to figure out if an earthquake is happening. Phones need to be stationary—for example, on a tabletop or in a bag on the floor, not in the pocket of someone walking—to feel an earthquake.
The system quickly determines the location and magnitude of an earthquake and then sends alerts to phones. All Android phones in the affected region receive alerts.
Nine seconds after the earthquake started underground
The system received enough data from the phones to detect an earthquake and send the first warnings.
The epicenters of earthquakes in Venezuela were located under densely populated areas. Within three seconds, the phones felt the P-waves of the first earthquake, said Mark Stogaitis, Google’s principal engineer who works on the early warning system. Six seconds later, the system detected an earthquake and sent out the first warnings.
The system continuously receives and processes data, Mr. Stogaitis said. As an earthquake develops, the system often adjusts the magnitude, time, location, and warning zone. Google’s system sensed an increase in the strength of earthquakes in Venezuela, and “the alert area increased as the earthquake grew,” Mr. Stogaitis said. Seconds after the first quake, there was a second, stronger one, and more warnings were sent out.
“Because the seismic waves from both events overlapped each other, the system treated it as one big event, alerting those who felt shaking from both events,” he said.
Distance matters. The further people are from the epicenter, the more likely they are to receive an early warning, giving them more time to act before the aftershocks begin. It is more difficult to warn people near the epicenter in time; these alerts usually come when the shaking has already started.
15 seconds after the earthquake started underground
The system continued to collect data from the phones and sent alerts to the wider region, including Caracas.
Google sends out alerts for earthquakes of magnitude 4.5 and above, which are considered strong enough to cause damage. People receive different types of warnings based on the estimated magnitude of where they are. One emits a loud sound and uses emergency messages to tell people to take immediate action in areas of potentially strong shaking, another emits an audible signal to tell people to be prepared, and a third warns people to be careful in areas where less shaking may occur.
21 seconds after the earthquake started underground
Eventually the alerts reached millions of phones over a large area.
Two earthquakes in Venezuela were powerful – the first had a magnitude of 7.2, the second – 7.5. There was a second earthquake the most powerful to strike the country since 1900. Google said a full range of alerts had been sent out. Nearly 1.4 million of the most severe warnings, which the company calls “Take Action,” were sent to people in areas where the tremors were strongest.
About 70 percent of all smartphones in the world run on the Google Android operating system. According to paper published in 2025 Google began sending out alerts for earthquakes detected by Android phones in 2021, initially in New Zealand, Greece, Turkey, the Philippines, and Central Asia. By 2023, it has expanded to 98 countries.
It is too early to say whether those early warnings saved lives on Wednesday. But a few seconds can give people enough time to take action to protect themselves. Most countries recommend that people “lower, cover and hold” before shivering.
Mr. Flores and his family, who were alerted while driving in Caracas, were initially confused, even after the tremors began. This is the first time they have received such a notice.
“We thought the road was really bumpy, which is normal for Venezuela,” he said. “Then we saw the street lights dancing and realized it was really serious.”
Now that he knows about the warnings, Mr. Flores said, he feels he will be better prepared to act if he receives one in the future. “It is very useful to get a warning, as it seems that it almost predicted the earthquake,” he said.
