https://techcrunch.com/2020/04/10/apple-and-google-are-launching-a-joint-covid-19-tracing-tool/

Apple and Google’s engineering teams have banded together to create a decentralized contact tracing tool that will help individuals determine whether they have been exposed to someone with COVID-19.

Contact tracing is a useful tool that helps public health authorities track the spread of the disease and inform the potentially exposed so that they can get tested. It does this by identifying and ‘following up with’ people who have come into contact with a COVID-19 affected person.