SANTA MONICA (CBSLA) — Even before Caltech got the heads up on Thursday’s magnitude-5.3 earthquake 10 seconds before it hit, Alissa Walker was already preparing to drop, cover and hold on.

According to the Curbed LA writer’s tweet, Walker had a 38-second warning.

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As an early adopted of the app QuakeAlert, she also got a map that showed, not only where the epicenter was, but also that it was 7,905 meters from her location.

“I got a warning, it said I was going to feel it, and I did feel it,” Walker told CBS2 News. She got early beta access to the app after writing about it for Curbed.

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“A scary day for some, but for us it was a good day,” said Josh Bashioum. He is the founder of Early Warning Labs, the company that developed the app being rolled out in Southern California.

“When you look at what we actually do here in L.A., we notify Metro, and they’ll actually slow and stop all their trains, and it can do that in about half a minute,” explained Bashioum. “If we can do that, we can prevent derailment.”

According to the website LiveScience, “The app works thanks to a network of seismic sensors that detect P-waves — the first energy that radiates from an earthquake. […] Once the longitudinal P-waves (short for pressure waves) are detected, the app sends a warning before the more powerful S-wave, or shear wave, arrives, which usually causes the most damage.”

Bashioum said Thursday’s temblor is a perfect example of how the early warning system can work. It not only told people exactly exactly how much time they had before it arrived, but it also let them know it was going to be a weak earthquake, which probably prevented some panic.

“If we got an alert right now and it said ‘extreme shaking,’ we’d move away from this old building,” said Bashioum. “But if it was light shaking, we’d probably kind of sit here and giggle and enjoy the shake, so it’s really, really important to know the level of shaking.”

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People wanting to sign up for a beta version of the app can sign up at the QuakeAlert website, though there is a waiting list to join.