Jose Flores was driving with his family to Caracas, Venezuela, on Wednesday to see “Toy Story 5” when a loud earthquake alarm sounded on his wife’s Google Android phone. Six seconds later he felt the earth begin to shake.
Venezuela does not have its own national early warning system, but people with Android phones received alerts from Google’s earthquake warning system, which can pull data from more than two billion phones equipped with built-in accelerometers. The same sensor that detects the rotation of the screen can also detect vibrations from seismic waves.
Three seconds after the underground earthquake began
Seismic waves reached the surface and were picked up by phones.
Google said the system, which is available in nearly 100 countries, sent out alerts on Wednesday that reached 11.4 million people, giving users seconds or up to two minutes notice of back-to-back strong earthquakes.
Several countries including Japan, Mexico, Canada and the United Stateshave state early warning systems. These rely largely on widespread regional networks of underground sensors that can detect earthquakes and send alerts to most phones – iPhone or Android – via government alarm settings, which are often enabled by default.
When earthquakes occur, they emit two types of waves that travel at different speeds. The faster-moving and milder primary waves, or P-waves, travel at a speed of 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 produce tremors.
When P waves begin radiating from the epicenter, Android phones detect the vibrations, begin collecting data, and send it back to Google servers for processing. The servers use information from many phones to figure out if an earthquake is occurring. To sense an earthquake, the phones must be stationary – for example, on a table or in a bag on the floor, rather than in the bag of a person walking around.
The system quickly estimates the location and magnitude of the earthquake and then sends alerts to cell phones. All Android phones in the affected region will receive the alerts.
Nine seconds after the underground earthquake began
The system had processed enough data from phones to detect an earthquake and send out the first warnings.
The epicenters of the earthquakes in Venezuela were below densely populated areas. Within three seconds, phones picked up the P waves from the first quake, said Marc Stogaitis, chief engineer at Google who works on the early warning system. Six seconds later, the system detected an earthquake and sent out the first alarms.
The system continuously receives and processes data, Mr. Stogaitis said. As an earthquake develops, the system often adjusts its magnitude, time, location and alarm area. Google’s system detected the increasing magnitude of earthquakes in Venezuela and “the alert region grew with the magnitude of the earthquake,” Stogaitis said. A few seconds after the first quake, a second, stronger earthquake occurred and more alarms were sent.
“Because the seismic waves from both events overlapped, the system treated it as a single large event and alerted those affected by the tremors from both events,” he said.
Distance is important. 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 tremors begin. It is more difficult to warn people near the epicenter in a timely manner. These warnings usually come when the shaking has already started.
15 seconds after the earthquake began underground
The system continued to collect data from phones and send alerts to a larger area that included Caracas.
Google sends alerts for earthquakes of magnitude 4.5 and above, which are considered strong enough to cause damage. People receive different types of alerts depending on the estimated severity of where they are. One makes a loud sound and uses urgent messages to urge people to take immediate action in areas where there may be extreme tremors, another beeps to alert people to be ready, and a third warns people to be vigilant in areas where minor tremors could occur.
21 seconds after the underground earthquake began
The warnings eventually reached millions of phones over a large area.
The two quakes in Venezuela were strong – the first was a magnitude 7.2 and the second was a magnitude 7.5. The second earthquake was the most powerful attacking the country since 1900. Google said it sent out the full range of alerts. Nearly 1.4 million of the most severe warnings, which the company calls “take action” alerts, went out to people in areas where the intensity of the shaking was strongest.
An estimated 70 percent of all smartphones worldwide run the Google Android operating system. According to a, the earthquake detection system works wherever people use phones, even in countries without other alarm systems Paper released in 2025. Google began sending alerts for earthquakes detected by Android phones in 2021, initially in New Zealand, Greece, Turkey, the Philippines and Central Asia. By 2023, it has been expanded to 98 countries.
It’s too early to tell whether those early warnings saved lives on Wednesday. But several seconds can give people enough time to take action to protect themselves. In most countries, it is recommended to drop, cover and hold yourself before the shaking begins.
Mr. Flores and his family, alerted while driving in Caracas, were initially confused, even as tremors occurred. It was the first time they had received such a warning.
“We thought the road was really bumpy, which is normal in 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 says he will be better prepared to take action if he receives one in the future. “It’s very helpful to get the warning because it seems like it almost predicted the earthquake,” he said.
