Monday's magnitude 5.2 temblor marked another success for California's earthquake early warning system, with users in some areas saying they received alerts on their phones before they felt shaking.

Monday’s magnitude 5.2 temblor marked another success for California’s earthquake early warning system, with users in some areas saying they received alerts on their phones before they felt shaking.

A screenshot of a Wireless Emergency Alert — similar to an Amber Alert — warning of incoming shaking. (Robert de Groot / U.S. Geological Survey) Monday's magnitude 5.2 temblor marked another success ...