what i dont get is, if you have a positive covid test, shoul you not stay home and isolate? so the app is really for the possibility that you came into contact with someone who would LATER test positive for covid, and MIGHT have been infectious when your phones were proximal to each other? does the app take into account the actual duration of time spent close to each other? is it 5 seconds or minimum 5 mins? how close? if you were 2 meters apart outside wearing masks with someonne for 3 minutes, and that persons gets a positive test 10 days later, do you get a notification? sounds like there will be a lot of people sent for testing unnecessarily.
There are "specs" for what defines "close contact". For example the CDC specifies less than 6 feet for 15 minutes. I do not know what thresholds they have set for Covid Alert but I suspect they are similar
It's quite simple. If I test positive, I register my diagnosis and everyone that was within say 6 feet for 15minutes, in the last X days, gets notified and therefore should go get tested. If I don't register my positive diagnosis, the system does nothing useful.
BTW, people saying GPS should be used need to understand GPS is accurate to 5m in good environments and worst in bad environments. Not good enough.
People that don't trust the app should know this has been put into Open Source so anyone can see how it is implemented.
There would be some very simple things they could implement that would tell you how "well behaved" you are. For example, tell me how many unique people I was within 6 feet, more than 15minutes. Even if I don't know if they had Covid or not. I would expect this to be very small. If it's 100, I know I am at risk, regardless if any of them tested positive and therefore I should change my behavior, if possible.