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.The proposed law could reach well beyond the borders of California. Because of the difficulty and added cost of producing handsets solely for sale in California, it could serve to make kill-switch technology a standard feature on phones sold across the U.S.The snatching of smartphones, often at knife or gunpoint, has become one of the biggest types of street crime across the country. It accounts for around half of all street crime in San Francisco, according to Gascón's office.Gasc