It started one minute before the shaking reached the capitol.
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"It was actually set up for the capitol, and if you actually lived on the West Coast, you were the early warning system," said Dr. Tom Heaton, seismologist at Caltech.
Mexico's system was installed after a devastating earthquake in 1985 that killed 10,000 people. Waves detected near fault lines outside Mexico City triggered the alarms that can be seen in a video tweeted out by a government official.
So why doesn't Los Angeles have a system like Mexico?
"In order for it to become a priority, we'd probably have to have some sort of damaging earthquake in the United States," Heaton said.
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After concerns that President Donald Trump planned to cut funding to the early warning system, Congress awarded $4.9 million each year to deploy the technology.
But Heaton said that is half of what should be put into the system and the timetable for implementation is unclear.
"It takes some time to actually put one of those things in place and to build it, it requires quite a bit of software development," he said.
The technology is already being used by BART in the Bay Area and it may be used by L.A. Metro in more than a year. The hope is that the system will be used to send Angelenos an alert on their phone.