A new law goes into effect on Wednesday that requires smartphones sold in California to have a “kill switch” to prevent theft.

But it’s already having an impact, with the inclusion of such protections on newer devices leading to a drop in smartphone theft. A recent study from the Consumer Reports National Research Center concluded that 2.1 million Americans had their phones stolen last year — a big number, but a 32 percent decrease from 2013. In New York, overall cellphone robberies are down 16 percent, with iPhone robberies down by 25 percent. (Apple was among the first to add anti-theft protections.)

“This is validation of what we knew to be the case all along, that if you remove the value of a stolen device you remove the incentive to engage in this violent behavior,” said San Francisco District Attorney George Gascón, a proponent of the anti-theft protections. “This wasn’t just a local problem, this was a global epidemic, and it seems we’re poised to see a dramatic reduction in violent robberies as this technology is implemented ubiquitously.”

Gascón was part of a global effort known as the Secure Our Smartphones initiative that pushed the industry to include protections, such as the activation lock feature that Apple added to the iPhone.

The California law, signed by Governor Jerry Brown last August, requires all phones sold after today to include some sort of technology allowing consumers to identify their devices as stolen and prevent them from being reactivated. The cellphone industry has voluntarily agreed to implement the protections nationwide, with Apple, BlackBerry, Google, HTC, Huawei, LG, Motorola, Microsoft, Samsung and ZTE all on board, as well as the major cellular carriers.

“Today’s fulfillment of the Smartphone Anti-Theft Voluntary Commitment is another example of the wireless industry proactively working together with policymakers and law enforcement to help protect consumers’ smartphones in the event they are ever lost or stolen,” said Meredith Attwell Baker, CEO of CTIA – The Wireless Association. “As media reports indicated from San Francisco to New York City, these efforts are significantly reducing device thefts across the country.”