The system buzzed through a half a million phones ahead of a 6.2 magnitude earthquake that hit Northwest California. It’s the largest quake since the system, called ShakeAlert, rolled out across the entire state.

People living there get alerts through the myshake app or the wireless emergency alerts system on their phones. Alerts also go out to Android users through a partnership between Google, USGS, and the California office of emergency services.

The quake did n’t do major damage to the area, and there were no fatalities. People reported getting alerts around 10 seconds before shaking started.

The system was in place in Los Angeles when a 6.4 magnitude earthquake hit 150 miles outside of the city. Users complained they did n’t get an alert even though they felt shaking. The app’s developers lowered the threshold before the state-wide rollout.