https://www.siliconvalley.com/2020/12/07/california-rolls-out-new-app-to-alert-you-to-covid-19-exposure/

As California’s latest coronavirus surge spreads at a record-setting pace, state officials on Monday unveiled a new cell phone app aimed at curbing the number of Californians who may be unknowingly fueling the transmission of the fatal disease.

Starting Thursday, Californians will be able to opt into the new app — dubbed CA Notify — that will send notifications to their cell phones informing them if they have been in close proximity to someone who has tested positive for the virus.