Apple and Google have released long-awaited smartphone technology to automatically notify people if they might have been exposed to the coronavirus.

The companies said 22 countries are already planning to build voluntary phone apps using their software, though declined to specifiy which. The privacy-focused technology relies on Bluetooth to detect when someone who downloaded the app has spent time near another app user who later tests positive for the virus.

Many governments have already tried, mostly unsuccessfully, to roll out their own phone apps to fight the spread of the COVID-19 pandemic. Australias's COVIDSafe app has encountered technical problems on iPhones owing to its inability to operate in the background; users must leave their phones unlocked and the app running at all time for it to function. Some other government apps have used GPS to track people's location, which Apple and Google are banning from their new tool because of privacy and accuracy concerns.

Some public health agencies have been waiting to use the Apple-Google model, while other governments have said the tech giants' privacy restrictions will be a hindrance because public health workers will have no access to the data.