The smartphone “kill switch,” which California just passed into law, is one of those technological innovations whose benefit is so obvious, it's hard to imagine why anyone would be opposed to its implementation.
A kill switch allows smartphone owners to remotely disable or “kill” their phones, in the event that they are stolen. The ultimate intent, of course, is to discourage such thefts: thieves won't bother stealing phones which they know will be rendered useless.
A cynic might speculate: “It's because the phone companies figure 'Hey, if you can't get your stolen phone back you'll have to buy a new one, which means more money for us. Whoopee!'” Or perhaps there's a useful valid consumer-protection rationale, only the phone companies forgot to issue the press release explaining it.
In February 2014, Congress proposed a bill that would require kill switch options on all smartphones sold in the U.S.; this proposal has not made it into law.
But California is unwilling to wait for a national bill. This week the state passed a law mandating kill-switch options on all smartphones manufactured and sold in the state after July 1, 2015.
California is the second state to pass such a kill-switch law; Minnesota passed a similar one in May.
Even if your phone does have a kill switch option (or you buy a phone that does), remember: the mere fact that your phone has this option won't help you unless you actually activate it. It's like any other anti-theft device: the best and strongest lock in the world won't protect your stuff if you forget to shut the door.