Apple and Google shared a fair amount about their COVID-19 contact tracing plans with their joint announcement, but they still left some gaps. However, Apple has been willing to fill in a few of the blanks in a follow-up with The Verge. The company is aware of the limitations of Bluetooth and that tracing apps can factor in the duration of proximity into alerts to reduce the chances of false alarms. It may only warn you when you’ve been within proximity of a COVID-19 patient for a substantial amount of time. You may get an alert if there was an infected person on the same bus, for example, but not if someone happened to be walking by on the street.

The tech firm also provided more details of how the tracing API will work. When the feature is integrated at the operating system level, you’ll have to opt in to the API before it will start sending and receiving Bluetooth signals. And if you don’t have a supporting healthcare app right at that moment, you’ll still get the last 14 days of proximity events once you install that app.