Californian politicians have passed a law mandating a “killswitch” in all smartphones, allowing users to remotely disable the phone if it’s lost or stolen. It’s the first such law to require such a feature to be enabled by default.

Bill 962 says all phones that are manufactured after 1 July 2015 and then sold in California must have the killswitch. Exactly how it operates is up to manufacturers, but the key requirements are that the owner must be able to remotely disable the phone; a disabled phone must remain unusable even after a hard reset; and that only the original owner can reactivate the phone on a wireless network.

The bill has exemptions meaning that the original owner loses the right to disable the phone after selling it to a new owner, or surrendering it as collateral on a loan.

Apple, Google and Microsoft have already promised to build a killswitch into their operating systems from next year, while Minnesota became the first state to mandate killswitches in May.

However, the California law goes a step further as, unlike Minnesota’s, it says phones must ship with the killswitch already enabled, with owners then having the option of disabling it. Given California is home to around an eighth of the US population, manufacturers may well decide it’s now simplest to build and enable the killswitch into all handsets shipped to the US.

The politicians behind the new law argue that it will make stolen phones less valuable, in turn deterring thefts. Several police authorities in major cities have cited statistics showing that smartphones are the target of a significant proportion of thefts in public places, particularly those involving violence or the threat of violence.

However, critics of the killswitch — including many GaS readers who’ve commented on previous stories — raise concerns that there’s a risk of public officials finding a way to force manufacturers to trigger killswitches without the user’s request, for example to shut down communications among a group of protesters.