California's new earthquake early warning system successfully sent an alarm three seconds before a quake of 4.4 magnitude hit Pasadena.
While the earthquake caused little damage, he felt in a large swath of area.
CalTech seismologist Lucy Jones said she received the warning at her location seconds before the earthquake on Tuesday night.
The earthquake on Tuesday hit La Verne at 7:33 p.m. but it was felt from Ventura County to Orange County more than 100 miles away.
California's new early earthquake warning system successfully sent an alarm three seconds before a tremor of 4.4 hit Pasadena. In the image you can see the earthquake tremors map, which shows that it hit moderately the city of La Verne, with a light effect in the metropolitan area of Los Angeles
CalTech seismologist Lucy Jones reported receiving the warning (pictured) at her location seconds before the earthquake on Tuesday night
The amount of warning an area receives depends on how close it is to the epicenter of the earthquake.
"Out of nowhere, the room started to shake," Ruben Estrada, who was in class when the earthquake occurred at La Verne University, told KTLA.
"Desks were everywhere, people shouted, we were in a crazy panic, but everyone managed to get out safely."
The earthquake was followed by more than a dozen aftershocks and was the largest earthquake in the Los Angeles metropolitan area in three years.
Jones demonstrated how the ShakeAlert early warning system worked. The system began to ring loudly to warn that it was approaching.
The sound grew faster as it got closer and closer.
Many received the alert in a cell phone application called Quake Alert, which aims to send notifications to phones up to 60 seconds before an earthquake occurs.
But the application is still in the test phase, and not everyone received a warning on Tuesday night.
Many received the alert in a cell phone application called Quake Alert, which aims to send notifications to phones up to 60 seconds before an earthquake occurs. The image is an example of how an application warning message would be during an earthquake
CalTech University is one of the beta testers of the system, which is being developed by the US Geological Survey.
The early warning system is designed to quickly detect the start of an earthquake, calculate the level of expected earth tremor, and issue a warning, according to the California Integrated Seismic Network.
It works by detecting the first energy that radiates an earthquake, known as the energy of the P wave, which rarely causes damage.
The P wave information can calculate the location and magnitude of the earthquake and provide a warning before the S wave arrives, which is the one that causes the most damage.
While a few seconds of warning may not seem like much, it may be all in one big earthquake.
This is not the first time that the early warning system has worked. San Francisco received an 8-second warning before an earthquake of magnitude 6.0 hit Napa in 2014 (pictured)
A crack running through the center of a street damaged by the earthquake after Napa was hit
"This is enough time to slow down and stop the trains and the taxiing of planes, to prevent cars from entering bridges and tunnels, to get away from dangerous machines or chemicals in work environments and to cover themselves under a desk" , according to CISN.
Airports, oil refineries, pipelines, schools, universities, town halls and libraries on the West Coast are planning or already testing the system.
The West Coast map shows the amount of early warning time that might be available in an early warning detection system during future earthquakes
Hospitals in California are testing the system to give surgeons enough time to remove the scalpels from patients, while office buildings are rewired to automatically take the elevators to the nearest floor when the warning sounds.
The condos in the state are also being reconfigured so that residents have enough time to leave and take cover, according to the Los Angeles Times.
This is not the first time that the early warning system has worked.
Scientists at the University of Southern California received a 10-second warning before a 5.3 earthquake near the Channel Islands in April.
And San Francisco received an 8-second warning before an earthquake of magnitude 6.0 hit Napa in 2014.
The USGS has been developing the early warning system for years, but has had trouble finding funds.
President Trump tried to end federal funding for the program in one of his earlier proposals for the federal budget.
But Congress then approved a $ 1.3 billion budget project that included a contribution of $ 22.9 million to the system.
The USGS had previously promised that it would issue limited public warnings of the system by the end of the year, as long as the government did not cut the funds.
He hopes to install more sensors in Washington, Oregon and parts of rural northern California.
Similar systems are already in full swing in Japan and Taiwan and are being tested in central and southern Mexico.