"Kill switches" in smartphones are doing a great job bringing down phone theft in major cities, a press release from the New York attorney general's office states.

The feature, which lets owners deactivate a phone that is lost or stolen to make them useless, has resulted in phone robberies declining by 40 percent in London, 22 percent in San Francisco and 16 percent in New York, according to USA Today.

The press release comes two years after New York Attorney General Eric Schneiderman, London Mayor Boris Johnson and San Francisco District Attorney George Gascon started the Secure Our Smartphones initiative with the goal of lobbying smartphone companies to install kill switches.

iPhone thefts were also shown to have declined because of the kill switches, shrinking by 40 percent in San Francisco and 25 percent in New York from Sept. 2013 to Sept. 2014, Tech Times reported.

New York Police Commissioner William Bratton said it is no coincidence that smartphone theft has gone down since companies starting installing the feature in consumer mobile gadgets.

"Restricting the marketability of stolen cellphones and electronic devices has a direct correlation to a reduction of associated crimes and violence," Bratton added.

A new law in California will require phone makers to include a kill switch in all of their devices, BetaNews reported. Whether other states will pass a similar law remains to be seen.

Big tech companies that have updated their phones with kill switches include Apple, Samsung and Google, with Microsoft expected to do the same sometime this year, Tech Times reported.

"The wireless industry continues to roll out sophisticated new features, but preventing their own customers from being the target of a violent crime is the coolest technology they can bring to market," Gascon said.