How is this going to work if there is a lack of swab testing? Does each person complete a symptom checker? If no symptoms, I'm assuming you would update if you suddenly start symptoms. Would you record if you have a mild sore throat or runny nose, stomach ache, diarrhoea etc?
I love the assumption by the under-thirties who think up nonsense like this - that everyone in the world has a smart phone and uses it all the time.
The irony is, the people who are most open to infection are the older population, the least likely to have or use the technology their notion depends on!