https://www.vox.com/2020/4/24/21234762/apple-google-contact-tracing-coronavirus-lockdown

Apple and Google are collaborating on technology to monitor the contacts of infected people. Here’s how it works.

South Korea and the United States reported their first cases of Covid-19 on the same day. Yet while most Americans remain under stay-at-home orders, many in South Korea are doing what seems unthinkable in the US — returning to their offices.