Essentially this is an app that logs geospatial + timestamp all the time. Then on the app you can report that you’ve got a confirmed case, and it’ll flag all your locations for the last week, and correlate that with all the locations/times of other people on the system and send them an alert that they were within the potential infection zone.
Though my understanding of this stuff is pretty rough, I’m pretty sure virus’ are like proteins and can sit on a door handle forever (they don’t “live”).