Contact tracing—monitoring who’s getting COVID-19 and tracking down anyone who might have been in contact with that person so they can quarantine—has long been considered a key to slowing and eventually ending the pandemic.
Health departments around the country (and world) have been staffing up on human contact tracers. Meanwhile, in April, Google and Apple announced they were teaming up to develop a way to do the job through smartphones. The result, released in May, is the Google and Apple Exposure Notification system.