(Jennifer Abel @ ConsumerAffairs) Last August, California became the second U.S. state (after Minnesota) to pass a law mandating that all smartphones sold in the state come equipped with a “kill switch” option allowing owners to remotely disable, or “kill,” their phones if they are stolen. The process is also known as “bricking” – transforming the phone from a valuable piece of electronic equipment into a mere plastic brick.

The rationale behind kill switches is to discourage smartphone thefts: thieves won't bother stealing phones if they know the phones' legitimate owners will immediately be able to brick them and render them worthless.

Wireless carriers initially hesitant

Samsung developed a kill-switch app as early as 2013, yet companies including Verizon, AT&T, T-Mobile, United States Cellular Corporation, and Sprint responded by preventing Samsung from pre-loading the app. This in turn inspired New York's attorney general in December 2013 to ask those wireless carriers why they wouldn't allow it, and urged carriers to embrace the technology “as a simple yet effective way to protect” smartphone owners from theft.

The following March, the New York AG and San Francisco District Attorney's offices issued a joint statement announcing that Verizon and US Cellular (no mention of the other companies) had decided to allow the apps, which smartphone owners could activate for free.

Why would phone and wireless companies oppose kill switches in the first place? Industry representatives said it was to prevent hackers from exploiting the switches. Cynics speculated the reason might actually be “The phone companies all 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!'”

Phone thefts in decline

California's kill-switch law only came into force yesterday, yet a study published by Consumer Reports last monthsuggests that kill-switch technology is already having an effect: in 2013, 3.1 million Americans had their phones stolen, but in 2014 that number dropped to 2.1 million.

Consumer Reports noted that “The technology could eventually save U.S. consumers $3.4 billion” (which could also be interpreted as “The technology could eventually cost U.S. companies $3.4 billion in sales to replace stolen phones”).

Take additional steps to protect your phone

That said: even if your phone does now have a kill switch, don't make the mistake of thinking that alone is enough to protect your phone and whatever data is on it.

As Consumer Reports' study noted: “Kill switches aside, many phone owners do an abysmal job of protecting their mobile devices …. Among survey respondents, only 46 percent set a screen lock using a four-digit PIN or a stronger method such as a lengthy password or fingerprint. Just 33 percent backed up their data, including photos and contacts, to a computer or online service. Built-in security technology can only get a consumer so far—to reap the benefits, you actually have to use it.”

It's like any other anti-theft device: the best and strongest lock in the world still won't protect your stuff if you forget to shut the door.