Covid-19 in S. Korea @5:13
https://www.youtube.com/watch?v=BE-cA4UK07c
My opinion is those apps work because S. Korea remembers SARS-1 (2002/2003), and people there are cooperative. Also, if you do full contact tracing early enough, there aren't an overwhelming number of patients like NY.
S. Korea is the only country that literally "flattened the curve." See unbelievably flat graph @6:50 in link above.
(S. Korea had the same problem as Toronto with SARS-1, where the hospital doctors and nurses were wiped out by the first few cases. In S. Korea, it was the first SARS-1 patient wandering around town like a cruise missile to several doctors and hospitals that spread the disease, as nobody identified the magnitude of the problem.)
> And how will things work with an orderly supermarket queue, where law-abiding people stand patiently six feet apart?
In the SF Bay Area, here's how social distancing works at grocery stores:
1) one entrance/exit with security guards at the door
2) queue outside with shoppers 6' apart
3) only 50 people allowed in at one time, but distance is not enforced in the store except 6' in checkout lanes. However, American grocery stores are large, so the spirit is being followed. Recently, I've seen saran wrap over POS terminals. Bank ATMs also need that prophylactic. :)
4) shoppers are responsible for washing their carts and hands, which is a gap.