"The system then takes that the contact events were 'authentic' and then takes the transmit power and received signal strengths that each proximity event produc

"The system then takes that the contact events were 'authentic' and then takes the transmit power and received signal strengths that each proximity event produced (remember, these are broadly representative of physical distance), and runs those through a sophisticated risk model to work out the encounters that are high risk from a virus transmission point of view. " This is not possible. Other countries use humans (Contact Tracers) to do this, working with the person infected. Contact Tracer: On this day looks like blah happened, Infected: Yes I forgot. Infected: On this day I talked to this person for ages but I don't know them. Contact Tracer: I see, we will contact them. Fine, fine, move quick and break stuff. Don't think about it. In Australia- The App is not anonymous! It reuses the ID, they don't roll. 3rd Parties track away. iOS does not work at all. You have to have the phone unlocked and on the front. If you want to pretend that works, you'll make a great government consultant like the Australians used.