[g_p]

> I built an exposure notification app that solved the backgrounding issue by simply using the backend to reconstruct the missing Android -> iOS piece: https://medium.com/@dangish/a-solution-to-iphone-backgroundi....

An interesting approach here, although worth noting there are some privacy implications of this, since it requires "healthy and not ill" people to share their full list of contact events (or at least healthy iOS users). And Android users in your approach would need to check in for updates to "what they missed".

One thing I'm slightly unsure of is how well this would perform in reality - did you get this to work for two long-sleeping iPhones? That seemed to be the "edge case" that was the most challenging here, and I'm not sure what you're suggesting changes anything there?

[ridewinter]

A variety of countermeasures can be used to keep the app awake in the background, including restarting services and (more controversially) location.

And IMO, including a general/non-precise location of contact is incredibly useful for epidemiological purposes and to assist the manual contact tracing teams. The value far outweighing the hit to privacy.

In any case, Google-Apple are dictating how these apps need to be built and released, so private innovation doesn't seem welcome at this juncture.

[g_p]

Yep - location listeners can help keep apps open quite well on Android. Not sure about iOS.

RE rough location, the NHS currently asks people to enter the first "half" of their postcode, which gives a broad approximate geography, but still is a large area with a large population (probably up to 100k people). This also lets the NHS get an idea of app adoption throughout the country, which will help them know how much attention to give app-based contact tracing on a more localised basis, compared with alternative approaches and the old-fashioned "ask the person for names and phone numbers, and call them up".