Read on Twitter
NHS Covid-19 app: How England and Wales' contact-tracing service works some very clear info from @LeoKelion here https://www.bbc.co.uk/news/technology-54250736
I have some queries I may report back on. Its not exactly a simple, self explaining app tho.
Ok heres one chain of thought. The app sends advice to a user who's scored above 900 as a risky contact to isolate, but the user remain anon cos its a Gapple decentralised app. So far so good.
However the user on receiving warning fails to self isolate and this later comes to light perhaps through manual tracing activity or because user ends up receiving treatment. Can the app warning be obtained by police as evidence for a fine? Can it be deleted by user ( I hope so)
Do we only regard someone as having legally received advice to self isolate if they receive a positive test, as opposed to those who got warnings? If they got warnings and have symptoms? has this been clarified? Not clear from BBC report.
This isn't an alarmist comment. Just wondering about the various perverse incentives here. The possibility of being in a place where you feel you can't isolate - maybe financial worry - and are scared of being " caught" might discourage uptake of the app. Police powers might..
..also be discriminately used against BAME communities as has been the pattern with precious use of police powers during the pandemic. But BAME communities are most in need of protection from virus spread.
Otoh we desperately want the app to be used to maximise self isolation! This is all q difficult & why i hope there's been some serious behavioural attitudes and manipulation work done on this , as I said on @BBCWorldatOne .
Point 2 ; testing delays. If person A with symptoms gets a positive test, then at that point their exposure notifications are uploaded. If it takes 7 days to get the test result then we don't warn person B a stranger exposed to A in the 7 days or so prior, with no symptoms yet
This is ok if A isolates while waiting for the test result. I think. But will they? Will their employers let them? We already have stories of teachers being told to go in even if they had minor symptoms and were waiting for a test.
Tough stuff. Stay safe out there 
Ps these are real queries and Im not sure if i have the testing timing right - any info very welcome! @tforcworc do you know how many days ENs are uploaded on positive test? I looked at https://www.gov.uk/government/publications/nhs-covid-19-app-privacy-information/nhs-covid-19-app-data-protection-impact-assessment#overview but dont see it.
