SAN FRANCISCO (KPIX 5) — Over the last few years, there has been an epidemic of cellphone robberies in San Francisco. Thieves violently attacked people for their smartphones – often in broad daylight.

Those crimes aren’t happening nearly as often, these days, thanks to Apple’s kill switch technology.

San Francisco District Attorney George Gascon says the kill switch is curing the epidemic.

“We knew that this could be fixed, and it has been fixed,” he said.

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Gascon says iPhone thefts are down 40% in San Francisco since Apple put a kill switch on the iPhone 6. Smartphone thefts are down 27%.

“We immediately saw a modification of behavior on the street – as thieves were taking phones, they realized they could not put the phone to use,” he said.

Those iPhones once worth big bucks on street, are now worthless. Thanks to the fingerprint recognition technology and iCloud fix those stolen phones are basically pretty paperweights.

The statewide kill switch law goes into effect July 1, and Gascon hopes the problem shrinks even further once all smartphones are covered. The value of the shut-off feature will increase exponentially as smartphones evolve from being calling and texting devices, and become actual lifelines.

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“This device is now full of so much personal data – medical data, banking data that it would have a bad impact if somebody else gets a hold of it,” he said.

Gascon said it’s not just in San Francisco. The mayors of New York and London tell him they are also seeing a dramatic drop in smartphone thefts.