First launched in the US, Google is now expanding its Android-based earthquake detection and alert system to Greece and New Zealand. Users will get warnings of earthquakes on their phones, giving them time to get to safety. The earthquakes won’t be detected by seismometers but by the phones themselves.

It’s the first time the tech giant will handle everything from detecting the earthquake to warning individuals. Mobile phones will first sense waves generated by quakes, then Google will analyze the data and send out an early warning alert to the people in the affected area. Users will get the alert automatically, unless they unsubscribe.

When it launched the service in California, Google first worked with the US Geological Survey and and the California Governor’s Office of Emergency Services to send out earthquake alerts. This feature later became available in Oregon and will now expand to Washington in May – and eventually to even more states in the US.

Mobile phones are already equipped with an accelerometer, which can detect movement. The accelerometer can also detect primary and secondary earthquake waves, acting like a “mini seismometer” and forming an earthquake detection network. Seismometers are devices used to detect ground movement.

Traditional warning systems use seismometers to interpret an earthquake’s size and magnitude, sending a warning via smartphone or loudspeakers to residents. Even if they come seconds before the quake hits, these warnings can buy valuable time to take cover. But seismometers can be difficult and expensive to develop.

That’s why a warning system that can rely on smartphones has a lot of potential. Richard Allen, a seismologist at the University of California, Berkeley, told Science that Google’s interest in building quake-sensing capabilities directly into Android phones was an enormous opportunity, or, as he calls it, a “no brainer.”

“It’d be great if there were just seismometer-based systems everywhere that could detect earthquakes,” Marc Stogaitis, principal Android software engineer at Google, told The Verge last year. Because of costs and maintenance, he says, “that’s not really practical and it’s unlikely to have global coverage.”

Earthquakes are a well-known threat in Greece and New Zealand, where Google’s service is being deployed. Greece is spread across three tectonic plates, while in New Zealand, the Pacific Plate collides with the Australian Plate. Neither country has deployed an operational warning system, which created an opportunity for the tech giant.

Caroline Francois-Holden, an independent seismologist who until recently worked at GNS Science, told Science that many earthquakes in New Zealand originate offshore, where few phones are found. This might make Google’s system less than ideal. “Any earthquake early warning system needs to be designed with that in mind,” she said.

There are other limitations, too. Those closest to the earthquake won’t get much advance warning since they’ll be the first ones to detect the quake. But their phones will help give a heads-up to others farther away, giving them crucial time to take shelter. But as Android is the leading OS system for smartphones, this service probably has a lot of room to grow.