Following Apple’s lead, Google and Microsoft will add “kill switches” to their next smartphone operating systems — a measure that has apparently led to a sharp drop in thefts of iPhones.

The announcement was made Thursday by New York Attorney General Eric Schneiderman and San Francisco District Attorney George Gascon, who head a Secure Our Smartphones Initiative that has steamrolled initial opposition from the wireless industry with a campaign backed by law enforcement.

“This is very significant and validates everything we have been trying to do legislatively in Sacramento this past year,” said State Sen. Mark Leno, D-San Francisco, who has introduced a bill requiring every smartphone maker to have a kill switch.

A kill switch lets an owner remotely deactivate a stolen smartphone, rendering it useless until it is reactivated by its owner.

The move means that next year, the new versions of operating systems used by 97 percent of smartphones in the U.S. will have the anti-theft technology. About 3.1 million smartphone-related thefts were reported last year in the U.S., double the number in 2012, according to Consumer Reports.

In the first five months of this year, thefts of Apple devices fell by 17 percent in New York City while thefts of Samsung devices — without a switch — increased 51 percent from the same period a year earlier, according to new crime statistics in a report released with the announcement.

In San Francisco, thefts of Apple devices fell 38 percent, the report said.

But the battle is not over. The next step, according to the report, will be to make the anti-theft software part of the default operating system so the user doesn’t have to choose to activate it. Apple’s kill switch requires the user to activate it. A spokesperson for Gascon said the same will be true for Google’s and Microsoft’s.

“Because kill switches are only available on an opt-in basis, not enough consumers are signing up,” according to the report. “This underscores the urgency of (our) call to make kill switches a standard opt-out function on all phones.”

There are sharp divisions over which is best among proponents of some form of kill switch. Some say opt-out is best because most users will go with the default mode; others say users should be free to choose whether they want to use the feature.

Leno’s bill would require opt-out and has met opposition from some industry and advocacy groups. It has passed the Senate and has been working its way through various Assembly committees.

Leno said opt-out is necessary because “the deterrent, to be fully effective, must be ubiquitous. If it’s something you have to do as a consumer, the criminal is going to say my chances are 50-50” of getting a phone without a kill switch, he said.

Adi Kamdar of the Electronic Frontier Foundation disagreed.

“We think opt out isn’t the best way to approach any technological solution,” he said.

Apple’s kill switch, called an Activation Lock, works after the user turns on the operating system’s Find-My-iPhone feature. Mountain View-based Google, whose Android operating system runs on more than half of all smartphones in the U.S., said it would soon release details of its switch.

Microsoft, of Redmond, Wash., said its anti-theft feature will be offered as an update for phones running Windows Phone 8.0 and newer. Nokia phones run on Microsoft’s operating system.

Microsoft vice president for government affairs Fred Humphries said in a blog that Microsoft’s kill switch will include the ability to remotely erase personal data, render the smartphone inoperable by unauthorized users and prevent reactivation or setup without the authorized user’s permission.

Kill switches “make a lot of sense,” said Ken Dulaney, a mobile analyst with Gartner. “We have to stop people stealing phones. But if it’s not done well and causes a lot of support calls to carriers, it’s not going to help. If it’s done properly, it’s a great thing to have.”

The announcement is a big win for the initiative led by Schneiderman and Gascon, which has been racking up successes lately.

In September, three months after the initiative kicked off, Apple introduced its Activation Lock. Earlier this year, federal legislation was introduced requiring carriers and manufacturers to add anti-theft capabilities to smartphones. In April, CTIA, the wireless industry trade group, abandoned its opposition to the proposal.

Contact Pete Carey at 408-920-5419 Follow him on Twitter.com/petecarey.