Apple and Google on Friday announced a joint effort to notify people via smartphone — on an opt-in basis — if they've come into contact with someone with the coronavirus, without having to share users' location information with government authorities.

Why it matters: Contact tracing is seen as a key means for allowing society to reopen from shelter-in-place orders, but there have been significant privacy concerns about requiring people to share their location and other personal data with the government.

The big picture: Apple and Google have spent the last decade mostly driving wedges between their respective mobile operating systems but are launching this unprecedented collaboration as countries around the world eye technology solutions to track the spread of COVID-19. The companies aim to offer the maximum public health benefit without sacrificing individual privacy.

What's next: Apple and Google are implementing the necessary software in two phases.

In mid-May , the companies will update their operating system to support the contact-sharing technique and allow for contact-tracing apps.

, the companies will update their operating system to support the contact-sharing technique and allow for contact-tracing apps. In the coming months, a further operating system update will allow the system to work with out needing a specific app.

How it works:

Google and Apple are both making changes to their mobile operating systems to let devices exchange a private key with nearby smartphones via Bluetooth, logging any time users come in close proximity.

If someone tests positive for COVID-19 and enters that information into an app, 14 days worth of their contacts with other users are sent to a server.

Phones periodically check if any recently encountered user has reported being infected. If so, a notification pops up letting the user know that someone they have been in contact with has tested positive and more information is provided.

The new technology will work on iPhones running iOS 13 or later and on Android devices running any version of the operating system from 2015's Marshmallow on.

The companies say they have taken a number of steps to protect user privacy, including:

Allowing individual choice whether to use the technology.

Not collecting location or other personally identifiable information.

Not allowing the actual list of people a user has been in contact with to leave the phone unless desired.

Pledging the tool will only be used for contact tracing by public health authorities for COVID-19 pandemic management.

Not identifying people who test positive to other users, Google or Apple.

Retaining the ability to disable the broadcast system on a region-by-region basis when it is no longer needed.

The bottom line: Centers for Disease Control and Prevention director Robert Redfield, echoing other public health officials from around the globe, told NPR Thursday that contact tracing is vital to curbing the spread of the coronavirus and preventing recurring localized outbreaks.