Kill-switch technology that can render a lost or stolen smartphone useless would become mandatory in California under a new bill that will be proposed to the state legislature in January.The bill will be introduced by Senator Mark Leno, a Democrat representing San Francisco and neighboring towns, and George Gascón, the district attorney for San Francisco. Gascón has been spearheading a push by major law-enforcement agencies across the U.S. for more to be done to prevent smartphone theft.