Updated with additional reporting on kill switch plans for Google and Microsoft.
For several years, cellphone theft has been a growing epidemic worldwide. But the police in New York, San Francisco and London say they are finally starting to see a dip in thefts of one of the most popular smartphones.
The reason? The attorney general of New York, Eric T. Schneiderman, and the district attorney of San Francisco, George Gascón, share the theory that phone thefts are dropping because of Apple’s addition of a so-called kill switch, a type of antitheft technology, in its iPhone in September.
Police officers in San Francisco and London say that after Apple introduced its measure, called Activation Lock, last fall, iPhone theft fell significantly. Comparing data in the six months before and after Apple released the feature, the police said iPhone robberies in San Francisco dropped 38 percent, and those in London fell 24 percent.
The police in New York said that robberies involving Apple products dropped 19 percent and those involving grand larcenies dropped 29 percent in the first five months of 2014, compared with the same time period from 2013.
A kill switch is software that lets consumers lock down a phone after the device has been reported stolen; users can reactivate the phone only with the correct password or personal identification number. Police have said that this type of antitheft technology could discourage criminals from stealing smartphones.
Microsoft on Thursday said that it, too, will introduce a kill switch in a future software update for its Windows Phone operating system. Google will also be introducing one in the next version of Android, said Matt Kallman, a Google spokesman.
“The introduction of kill switches has clearly had an effect on the conduct of smartphone thieves,” Mr. Schneiderman said in an interview. “If these can be canceled like the equivalent of canceling a credit card, these are going to be the equivalent of stealing a paperweight.”
Other factors could have contributed to the decrease in iPhone thefts. For one, the police and tech companies have tried harder over the last year to educate consumers on additional security measures to protect phones, like setting up passcodes, which can make it harder to gain access to devices so that they can be erased and resold.
Over the last year, several lawmakers across the country have pushed for stronger antitheft features on smartphones. In May, Minnesota became the first state to require a kill switch on all smartphones. In California last month, senators passed a billrequiring phones sold in the state to include the antitheft technology. That bill still requires approval from the governor of California, Jerry Brown.
San Francisco’s district attorney, Mr. Gascón, has been one of the most vocal supporters of a kill switch. He and Mr. Schneiderman collaborated to form the Secure Our Smartphones initiative to press businesses to create a technical way to dissuade thieves from stealing phones.
Mr. Gascón said plenty of work remained. He said he hoped all manufacturers would include a kill switch turned on by default on all smartphones so consumers did not have to figure out how to use it. In the iPhone, for example, it is not turned on by default.
“Many consumers might not be tech-savvy enough to do this,” Mr. Gascón said. He added that he still thought it was necessary for there to be laws requiring kill switches in phones, similar to how seat belts eventually became legally required inside cars.