When experts first started talking about using contact tracing apps in order to keep the spread of coronavirus under control, lots of people expressed reservations about just how much such an app might infringe on their privacy. And now that a few countries have already instituted these apps, it would appear that those fears are indeed valid.
Contact tracing apps are normally downloaded onto people's phones, and when a user comes into contact with a person who tested positive for the virus, they receive a notification informing them of their exposure and advising them to quarantine at home for two weeks.
Authorities will know who does not comply because most of these apps will notify them if a person who is supposed to be quarantining goes outside of a certain perimeter around their home. And leaving the phone at home is not a viable option because these apps are also required to enter businesses like grocery stores.