There are some tourists who arrive at CT international airport. On arrival they need to prove they have had a negative covid test in the last 72 hours and that they have the Covid Alert app installed on their phones.
They comply and start their vacation. They make their way to Knysna and go to local restaurants as tourists do. Unknown to them a day before arriving in Knysna they contracted the virus.
While out dinning, they are pre-symptomatic and at some restaurants they begin to shed virus. Everyone at the restaurant and they are completely unaware of this all playing out. (See Adults With COVID-19 Twice As Likely To Have Eaten At Restaurants, CDC Study Finds)
You decided that because of all kinds of stories you have seen on Facebook, not to install the Covid alert app. So there is no digital handshake that happens between your app and theirs. [NOTE: A digital handshake between apps happen when they are in a 2m proximity for longer than 15mins. See these FAQ’s]
Two days after being in the same restaurant as you they begin to develop symptoms and go for a COVID-19 test. The test comes back positive. They then enter their positive status into the app and the app then smartly notifies all the people that have had a digital handshake with them that those individuals have been in close contact with someone that has tested positive for COVID-19.
Because you didn’t have the app installed you are completely unaware of this in the meantime they have also infected you but you are unaware of the exposure.
You decide to go to a family gathering, and at this gathering are elderly vulnerable individuals which you go on to infect. They end up having a severe form of the disease and 4 of them pass away. (See Coronavirus kills 4 family members and sickens others after a dinner in New Jersey)
Had you had the app installed on your phone you would’ve been notified of the tourists positive infection and you could then have quarantined yourself as suggested after an exposure. This would also then have prevented you from going to a family gathering where you infected the elderly vulnerable individuals resulting in a tragedy.
This is how the app works: Exposure Notifications System - Helping Health Authorities fight COVID-19