Google and Apple on Friday announced a joint effort to enable the use of Bluetooth technology to help governments and health agencies reduce the spread of the virus, with user privacy and security central to the design.

Across the world, governments and health authorities are working together to find solutions to the COVID-19 pandemic, to protect people and get society back up and running.

Since COVID-19 can be transmitted through close proximity to affected individuals, public health organizations have identified contact tracing as a valuable tool to help contain its spread. A number of leading public health authorities, universities, and NGOs around the world have been doing important work to develop opt-in contact tracing technology. To further this cause, Apple and Google will be launching a comprehensive solution that includes application programming interfaces (APIs) and operating system-level technology to assist in enabling contact tracing. Given the urgent need, the plan is to implement this solution in two steps while maintaining strong protections around user privacy, according to teh companies.

First, in May, both companies will release APIs that enable interoperability between Android and iOS devices using apps from public health authorities. These official apps will be available for users to download via their respective app stores.

Second, in the coming months, Apple and Google will work to enable a broader Bluetooth-based contact tracing platform by building this functionality into their operating systems so this contact-tracing software works without having to download an app. This is a more robust solution than an API and would allow more individuals to participate, if they choose to opt in, as well as enable interaction with a broader ecosystem of apps and government health authorities.

Apple’s iOS and Google’s Android have about 3 billion users between them, over a third of the world’s population.

Google said the technology will be distributed as part of its Google Play services, which are not available in China or on Android devices that do not use Google’s official version of the operating system.

Apple will distribute the technology as an update to its operating system, which many users enable automatically but not all.

Contact Tracing will alert participants of possible exposure to someone who they have recently been in contact with, and who has subsequently been positively diagnosed as having the virus.

The contact tracing using Bluetooth Low Energy will require explicit user consent. Google and Apple says that platform will not collect personally identifiable information or user location data, and that the list of people you’ve been in contact with never leaves your phone. In addition, people who test positive are not identified to other users, Google or Apple. The platform will only be used for contact tracing by public health authorities for COVID-19 pandemic management.

Here is how it works:

Let's say that Alice and Bob meet each other for the first time and have a 10-minute conversation. Their phones will exchange anonymous identifier beacons (which change frequently).

A few says later, Bob is positively diagnosed for COVID-19 and enters the test result in an app from a public health authority. With Bob’s consent, his phone will upload the last 14 days of keys for his broadcast beacons to the cloud.

Meanwhile, Alice continues her day unaware she had been near a potentially contagious person. At the same time, Alice’s phone periodically downloads the broadcast beacon keys of everyone who has tested positive for COVID-19 in her region. A match will be found with the Bob’s anonymous identifier beacons. Sometime later, Alice’s phone will receive a notification ("You have recently been exposed to someone who has tested positive for Covid-19.") with information about what to do next.

"Privacy, transparency, and consent are of utmost importance in this effort, and we look forward to building this functionality in consultation with interested stakeholders. We will openly publish information about our work for others to analyze," Google said.

Google and Apple have released draft technical documentation including Bluetooth and cryptography specifications and framework documentation.