ap photo In this 2018 file photo, an Apple logo is seen in raindrops on a window outside an Apple Store at the Country Club Plaza shopping district in Kansas City, Mo.

Apple and Google fueled hopes for digital technology’s promise against a fast-moving, invisible killer, announcing a joint effort to help public health agencies worldwide leverage smartphones to contain the COVID-19 pandemic.

New software the companies plan to add to phones would make it easier to use Bluetooth wireless technology to track down people who may have been infected by coronavirus carriers. The idea is to help national, state and local governments roll out apps for so-called “contact tracing” that will run on iPhones and Android phones alike.

The technology works by harnessing short-range Bluetooth signals. Using the Apple-Google technology, contact-tracing apps would gather a record of other phones with which they came into close proximity.

Such data can be used to alert others who might have been infected by known carriers of the novel coronavirus, typically when the phones’ owners have installed the apps and agreed to share data with public-health authorities.

Developers have already created such apps in countries including Singapore and China to try to contain the pandemic. In Europe, the Czech Republic says it will release an app after Easter. Britain, Germany and Italy are also developing their own tracing tools.

No such apps have yet been announced in the United States, but Gov. Gavin Newsom of California said Friday that state officials have been in touch with the companies as they look ahead at how to reopen and lift stay-at-home orders.

“We were on the phone just this morning, for example, with Apple,” he said at a news conference.

Privacy and civil liberties activists have warned that the apps need to be designed so governments cannot abuse them to track their citizens. Apple and Google said in a rare joint announcement that user privacy and security are baked into the design of their plan.

The technology might serve as a stopgap until there is widespread testing for the novel coronavirus, which in the U.S. remains limited after production problems and limited federal coordination of the tests’ production and distribution.

“It’s not a replacement for just having widespread testing, which would be more accurate,” said Tiffany Li, a visiting law professor at Boston University who studies privacy and technology. “But clearly we have a huge shortage of tests.”

Bluetooth signal tracking, as Google and Apple plan to use it, can protect privacy far better than other options such as GPS or cell-tower based location data, which allow centralized authorities access to the information.

But Li noted it could still lead to numerous mistaken alerts — for instance, if someone were in full protective gear or in an adjacent apartment while physically close to an infected person.