...you can now get pop-up notifications in some states if you were close to someone who later tested positive for Covid-19. The alerts come via state health department apps that use Bluetooth technology to detect when you (or more precisely, your phone) has been in close contact with an infected person's phone.

At least 15 states are taking part in this Covid-19 exposure notification system.
They include Alabama, Colorado, Connecticut, Delaware, Michigan, Minnesota, Maryland, Nevada, New Jersey, New York, North Carolina, North Dakota, Pennsylvania, Virginia, Wyoming and the nation's capital, Washington, DC.

Your phone can send you an alert if you were near someone who has coronavirus