Deprecated : this seems like a far better solution, too bad it is not open source https://www.novid.org

Track the germs not the person

A germ has a unique id, can have a timestamp and location.

You can leave germs, you can spot germs or record your movements.

In the event of sickness, you can review your germs and publish the ones that might have transmitted the disease. So other persons can check whether they were in contact with those germs and act. Track the germs not the person

A germ has a unique id, can have a timestamp and location.

You can leave or spot germs.

In the event of sickness, you can review your germs and publish the ones that might have transmitted the disease. So other persons can check whether they were in contact with those germs and act.

You need an app that can leave and spot germs. You also need a centralised database that your app can check for potential encounters with infected germs and publish yours in case you are sick (to increase anonymity, data can be aggregated by broader timeframes or location, infected germs can be put in crypographycal hashes where you can only batch query whether yours are part of it or not)

Recording your movement (if you want to do it) might be extra info the app can use to check whether you were close to infected germs. It can also be shared to the database (anonymising by aggregation) when you happen to be sick

Infected germs data might be aggregated into more coarser data that can then be made public. Government and NGO can also share time-geolocation infection data