Apple and Google have released a software tool that will allow nations to release coronavirus contact tracking apps that adopt the corporate privacy-focused model.
It offers developers access to additional Bluetooth functionality to solve a problem that existing iPhone apps sometimes fail to detect each other.
Android and iOS device owners will need to perform system updates.
But some countries - including the UK - are pursuing a different approach.
"The release of these APIs [application programming interfaces] together with OS updates it will be a key moment for the development and adoption of proximity tracking apps, "said Marcel Salathé, an epidemiologist at the Swiss research institute EPFL.
"In the future, our efforts must be aimed at ensuring interoperability between regions, which will now be considerably simpler [for] apps based on the same protocol. "
Apple and Google have said that public health agencies from 22 countries have already asked to test the API of their "exposure notification" system.
The app was not "a silver bullet", but "user adoption is the key to success and we believe that these solid privacy protections are also the best way to encourage their use."
Matching on the device
Contact tracking apps are designed to automatically record when two people approach each other for a significant period of time.
If one is subsequently diagnosed with coronavirus, the other may receive a warning, which may suggest that they self-isolate and / or require a medical test on their own.
But authorities believe that adoption has been hampered by two factors:
- is concerned that technology poses a privacy risk
- restrictions Apple places the use of Bluetooth by third-party apps in the background
In theory, the new system should address both of these problems.
Its "decentralized" approach identifies the correspondence of contacts on the devices themselves rather than on a centrally controlled computer server.
And this aims to reduce the risk of hackers or authorities using the database of who met whom and for how long for other purposes.
But the UK National Health Service and its counterparts in France, Norway and India say that the centralized approach provides them with a more in-depth view, making it easier to change the risk model that decides who receives the type of alert.
Apps that adopt the Apple and Google API can customize it within certain limits.
But they won't be able to record, for example, the coordinates of a phone's global positioning system (GPS).
"Not collecting certain types of data, such as location, is a political decision, not an engineering one," said technology consultant Benedict Evans.
"But Apple-Google has to create something for every phone on Earth, [potentially] including China and Iran, and think about how it could be abused.
"How much you need the extra data and whether it's worth risking privacy is a matter of opinion."
Austria was the first nation to launch a decentralized contact tracking app.
Stopp Corona, run by the Red Cross, has been downloaded over 600,000 times.
And its developers, Accenture, now intend to integrate Apple and the Google API for a June 10 update so that iPhone users no longer have to bring the app to the screen for it to work effectively.
But Stopp Corona currently offers users the ability to manually control when games occur - by pressing a button on the screen to activate a Bluetooth "handshake".
And this is not currently possible in the Apple-Google model.
So the developers plan to switch to using ultrasound audio ping in this situation.
The Apple and Google API is also currently incompatible with the way Stopp Corona triggers different types of notifications.
The app first serves a yellow alert if a contact self-diagnoses the virus and then follows a red or green alert depending on whether a medical test confirms it.
And the developers are working with Apple and Google to try and maintain this functionality.
"There is a really good collaboration on both sides," Accenture executive Christian Winhelhofer told BBC News.
"I am really interested in working on solutions suited to our needs."
Hugging couple
The next German Corona-Warn-App will also adopt the Apple-Google protocol.
But its developers have complained that unused phones only listen to a Bluetooth signal once every five minutes for a duration of about four seconds.
So, in theory, a couple hugging for three minutes, for example, might not be registered, while another would simply be touching each other at the right time.
Apple and Google are aware of this problem.
In contrast, the NHS app listens to a game approximately once every eight seconds.
The NHS has also developed an alternative solution to the iPhone's Bluetooth problem.
But he is still exploring the Apple-Google system as a backup plan.
