If I had any ability to execute ideas I would have made the app using raffle / cloakroom tickets as the metaphor.
Every time your phone sees another phone, they get one of your tickets and you get one of theirs.
Then whenever someone gets symptoms, if their ticket book was pink then the government announces “anyone with a pink ticket, stay inside for a week”.
(With real ticket books, there aren’t enough unique colours for everyone but the tickets do have unique serial numbers.)
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