Millions of people across California will participate in the Great California ShakeOut on Thursday, Oct. 17, a day dedicated to practicing earthquake safety.

The technology works with an early-detection earthquake warning system, the ShakeAlert. Managed by the U.S. Geological Survey, the early-warning system instantly notifies Metrolink when an earthquake is detected. Within seconds of the system sensing shaking, train conductors are told the magnitude of the earthquake.

You really don’t know when there’s going to be another significantly damaging earthquake, but we know it’s going to happen.”