By Adrienne Moore

SACRAMENTO (CBS13) – Questions surrounding last night’s earthquake near Lake Tahoe have shifted from “did you feel it?” to “did you get the Shake Alert?”

Within seconds, thousands of phones started chirping, but many others sat silent.

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If you have an Android device, the alert system is already built into the phone, but if you have an iPhone, or something else, a few other factors may have kept you out of the loop.

“My whole house just shook and I didn’t know what it was at first,” said Mark Cadena, who lives in Truckee.

Neither did people whose phones started dinging that danger was near.

“The ShakeAlert system, which operates really quickly, estimated the earthquake at magnitude 6,” said Robert de Groot, with the U.S. Geological Survey. “That was changed really quickly, within about a tenth of a second, and we brought it down to a 4.7.”

The quake, which hit 11 miles northwest of Truckee, was felt in Reno, Sacramento and Stockton, but the California Office of Emergency Services (Cal OES) says unless you have the state’s MyShake app, you may have missed it.

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“You can set the alert on the MyShake App to different thresholds, so sometimes the earthquakes will be above the thresholds set on individual phones,” said Brian May, of Cal OES.

The system, launched in 2019, uses 800 ground motion sensors to deliver warnings to people over their cell phones before the strongest shaking starts. How fast you receive an alert depends on how far away you are from the epicenter.

“It’s a great reminder that we drop cover and hold on,” said May. “It’s a great reminder that even a few seconds warning can be huge.”

Android devices are already equipped with a channel for the early earthquake warning system. Other users can turn on their wireless emergency alerts, which work even if you’re phone is in Do Not Disturb mode, but those alerts are only issued when a quake is a magnitude 5 or higher.

“Even seconds when you get these kinds of alerts can help people, wherever you are,” May said.

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More than 1.3 million people have downloaded the Shake Alert app. Cal OES said it expects and hopes that number will jump, especially after yesterday’s quake.

Adrienne Moore