Technology has come a long way in the 30 years since the Loma Prieta earthquake hit the San Francisco Bay Area, with no advanced warning, on Oct. 17, 1989. Sixty-three people died from the quake that also injured some 3,800 others, while also doing billions of dollars in property damage. There were no early warning systems back then. But Thursday, California unveiled the MyShake app that can provide alerts to millions of Californians.Here are three things to know about the earthquake warning app:1) How does the MyShake app work?You can get a shake alert by downloading the MyShake app to your cellphone. The app will alert users up to 20 seconds in advance of an earthquake in their area. “So this will allow people time, precious seconds, tens of seconds, to drop, cover and hold on before they feel the shaking,” said Stephen Hickman, director of the Earthquake Science Center for the U.S. Geological Survey. “It will allow people to move away from heavy shelves and machinery."2) How can this new app make a difference? Imagine undergoing a medical procedure and then hearing an earthquake alert.“If you're going to an optometrist and they've got a laser in your eye, to turn the laser off before the procedure to make sure we take care of those the most in need,” Gov. Gavin Newsom said. “Trains can be automatically stopped, alarms can be going off at schools, which will get kids to duck, cover and hold,” said Mark Ghilarducci, director of the Office of Emergency Services. “Firefighters' doors can open automatically because after an earthquake, a lot of doors get off kilter and they can't get the fire engines out, delaying their response. So there are many things that can be shut off or interrupted because we know that fires after earthquakes can be a huge problem.”The new app can even help prevent potential wildfires, according to Newsom.“To make sure we shut off -- and I am at peril at saying this -- a transmission line. I know you'll probably run with that," Newsom said. "I know I walked into it, but it is one of the benefits of the system that the utilities are connected to this system.”3) Is the system foolproof?It’s not perfect by any means, Newsom conceded. The system is activated only when a quake hits magnitude 4.5 or higher. “There is a seismic activity around 4.5, which is the trigger for the notification,” Newsom said. “And it was a little late or it didn’t come to your cellphone, we recognize this is a work in progress.”Why was 4.5 chosen as the metric? It’s because a 4.5 magnitude earthquake is when things start shaking.“At ground intensity 3, we’re going to see things falling off of shelves and possibly a book shelf falling over," Ghilarducci said. “So, when you correlate that with general magnitude -- it’s a 4.5.”The system relies on thousands of sensors placed in the ground. “The technology has been designed to detect that energy wave from the time it gets emitted to the time the shaking starts,” Ghilarducci said.The closer you are to the epicenter, the less time you’ll have to react.“If you’re standing right on top of the fault, where the epicenter is, you probably will get zero to maybe a second of warning,” Ghilarducci said. “But if you are further away, you should be able to get a few seconds -- up to 90 seconds of warning."California has already budgeted $16.3 million this year to get the MyShake app launched.