'Several countries are now considering using Bluetooth - the technology used for wireless earphones.
And Apple and Google announced on 10 April they were working together to provide a software building-block - known as an application programming interface (API).
But Apple is now locked in a row with France, which wants to gather more data than the technology giants plan to allow.
The Bluetooth model is also the basis of the UK's contact-tracing app, being tested at a Royal Air Force Base in North Yorkshire.'