Location history.  If you have Google maps, your location history is being recorded.

It is sitting up there in the cloud, right now, going back months or even years.

What if that could be put to use to track possible exposure to Covid?

An known infected person could voluntarily release the relevant section of their location history (already recorded due to the above).

From that we could go back in our own location history and see if we were possibly exposed, and take measures to prevent spreading it ourselves.

Location history faq from Google:

https://support.google.com/maps/answer/6258979?co=GENIE.Platform%3DAndroid&hl=en