California’s earthquake early warning system alerted more than 3 million people about the deadly Ferndale quake before shaking began Tuesday.

The 6.4 magnitude earthquake was reported around 2:40 a.m. about eight miles southwest of Ferndale in Humboldt County.

For millions of people near the epicenter, an alert was sent out to their phones up to 10 seconds prior to the dramatic shaking.

The alert notification reads “drop, cover, and hold on.”

It was sent out to an estimated 3 million Android phone users automatically through a partnership between California and Google. A quarter-million people received the warning through the MyShake app, a state-sponsored app developed by UC Berkeley that is available for download in the Android and iOS app stores.

In the hours since the devastating earthquake that killed two people and injured 11 more, the app has been downloaded more than 72,000 times.

Mark Ghilarducci, director of the California Office of Emergency Services, said preparedness is one of the most important things California residents can do to prevent loss of life during a powerful tremor.

“The single biggest threat we face to life and property in our state is a sizeable earthquake in one of our major metropolitan areas,” said Ghilarducci. “This earthquake was another important reminder for Californians to be earthquake prepared for the next big one.”

California’s Earthquake Early Warning System is the first in the nation and is managed by Cal OES.

The technology also has additional utility aside from alerting Californians, the state said. The early alert system is also being used in other emergency facets, including being explored as an early warning system to slow down nearby trains, recall elevators, open firehouse doors and shut off water and gas valves. It could also be used to close bridges and gates and notify hospital workers and educators.

In October, the early warning system was used to alert residents in the Bay Area about a 5.1 magnitude earthquake.

To learn more about the system and download the earthquake early warning app, click here.

To date, more than 2.2 million users have downloaded the MyShake app, the state says.