California has become the second state in the US to pass legislation that requires smartphones to have a ‘kill switch’ that can remotely block stolen phones from being reactivated, making them less valuable to thieves.

Minnesota passed a similar law in May  which goes into effect 1 July 2015.

The new law in California, signed by the state’s government on Monday, requires mobile phone makers to install a built-in, anti-theft mechanism in all smartphone sold after July 2015.

The Federal Communications Commission said more than 30 per cent of robberies in the US involve phone theft. In San Francisco, that figure is closer to 50 per cent.

An estimated 1.6 million smartphones were stolen in the US in 2012, according to Consumer Reports.

“Our efforts will effectively wipe out the incentive to steal smartphones and curb this crime of convenience, which is fueling street crime and violence within our communities,” said the bill’s author, Senator Mark Leno.

Over the last year San Francisco’s district attorney, New York’s attorney general and other law enforcement officials have been calling for handset makers to install a kill switch to combat rising smartphone thefts.

Operators in the US and the CTIA have expressed concern about this approach because they say it could also allow hackers to disable phones remotely.

Last year Samsung reportedly had pre-installed kill-switch software in some smartphones ready for shipment, but US carriers ordered their removal as a standard feature, CTV News reported.

Apple introduced the ‘activation lock’ in iOS 7 almost a year ago, which some security experts say was the first kill-switch that meets law enforcement’s desire to protect iPhone users.

Another reason mobile operators may not be enthusiastic about the prospect of a kill switch is that many smartphone users purchase insurance for $5 to $12 a month from operators or third-party providers like Asurion, which claims 20 per cent of mobile customers in the US have its coverage.