This story originally appeared on CityLab and is part of the Climate Desk collaboration.

On January 3, Los Angeles Mayor Eric Garcetti announced the release of ShakeAlertLA, a new earthquake-warning app for residents of Los Angeles County. The app—the first of its kind in the United States—promises to “save lives by giving precious seconds to you and to your family to take action and to protect yourselves,” Garcetti told reporters at a launch event at City Hall.

Available to download in both English and Spanish in the Apple and Google Play stores, ShakeAlertLA is designed to give smartphone users a warning, with sound, of earthquakes of 5.0 magnitude or larger, a few seconds or more before the shaking begins. That’s not a lot of time, but even a brief window can be enough to gather family members and “drop, cover, and hold on,” as earthquake drills instruct.

ShakeAlertLA

ShakeAlertLA was developed by the City of Los Angeles with the U.S. Geological Survey (USGS), AT&T, and the Annenberg Foundation. It grew out of the USGS’s larger ShakeAlert project for the West Coast, which has been under way since 2006 but delayed by federal funding cuts. Although ShakeAlertLA only works in L.A. County, the technology is open source, so other municipalities and developers can use it to make their own apps. (A separate USGS-partnered app called QuakeAlert, developed by the tech firm Early Warning Labs, is already available in beta.)

The new app depends on hundreds of sensors that collect data around geologic faults. When the sensors detect strong enough seismic activity, a notification is pushed out to users’ phones. The farther that app users are from the quake’s epicenter, the more advance warning they are likely to receive. Those very close to the epicenter may not be alerted until the shaking has already begun.