* people who own an Android or IOS smartphone to install a required app? (Might work if Google or Apple pushes the software, but does this outlaw non-stock-Android and IOS operating systems on a smartphone? Will Apple/Google do this for every country with an app?)
* people who don't own a smartphone to buy one? (Subsidized? Black-box devices that only need to be charged at home as an alternative for this group? How do you deal with people who don't want one for valid reasons besides privacy? E.g., people who got rid of them because they are vulnerable to the addictive properties of smartphone apps? And of course people who can't afford them.)
* people who can't use a smartphone to carry one around? (The digitally or otherwise illiterate or mentally incapable, and people with physical limitations won't just disappear overnight. This includes many elderly; exactly the weakest group with this virus.)