Is It Better to Do Person Based or Location Based?

I think the risk is in thinking that just because it works in places corea, we can do our version of this that provides additional protections. I am not convinced this is going to work here. And i think we need to recognize that there is a real trad off between something that works really effectively and something that requires more evasiveness with respect to privacy. So for example, do you make this thing voluntary or tory? The most obvious way in which this can be immediately porous, immediately ineffective, is if we made it voluntary and only a subset of the people used it. Would you make it voluntary, or would you make it mandatory?