Watching Your iPhone Work to Protect You from Covid-19

Much has been written about the Apple + Google Covid-19 Exposure Notification framework. This is the software that is now part of Android and iOS (13.5+) and powers Covid-19 detection apps for Android and iPhone like COVID Alert (much of Canada), COVIDWISE (Virginia) and dozens of other jurisdictions around the world .

I’m in Ontario and use COVID Alert on my iPhone 8 Plus. The apps are fantastic pieces of work from the Canadian Digital Service and its private sector partners Shopify and BlackBerry. That said, I have always wished for more feedback from the app itself. Something that gives me a sense of it actually working. I’m the first to admit that this isn’t a rational need. When you open COVID Alert here is what you see:

Great! You’re active! But what does that mean?

I’m grateful that no exposure has been detected! But the app doesn’t look like it’s doing anything. I know that that’s not the case. I know that it is doing stuff but that’s because I’m a nerd and because the Canadian Digital Service maintains the source for both the Android and iPhone COVID Alert apps on GitHub .

But how can I see it actually doing stuff?

Well here’s one way. Both iPhone and Android allow you to see a log showing each time COVID Alert has downloaded a list of exposures from the COVID Alert server.

On iPhone you can see the log in Settings -> Exposure Notifications -> Exposure Logging Status -> Exposure Checks .

A log of every time COVID Alert downloaded new exposures

A single log entry

Details for that exposure download event; COVID Alert received 246 IDs representing devices associated with a positive test.

What I believe this means is that in that one Exposure Check done at 10:09am ET COVID Alert downloaded 246 Tracing Keys (“device IDs”) of devices that had had a positive Covid-19 test reported over the past 14 days. It also determined that my iPhone did not get close enough to any of those phones, for a long enough period of time, to warrant me getting a Covid-19 test. It’s pretty cool to see the app at work.

What else could it do?

I would also love the app to help me understand:

  1. How risky is my current behaviour?
    How many devices did my phone see in the past 24 hours? How many rolling proximity identifiers (RPIDs) did my phone log? I know that you are not supposed to be able to derive a Tracing Key from an RPID, but could the system run a function over a set of RPIDs and estimate the number of unique Tracing Keys they represent?

  2. How effective is the app at warning people about potential exposure?
    We had 625 new cases of Covid-19 reported yesterday in Ontario. How does that compare to the 246 Tracing Keys my phone received? Do the time frames line up? Can I compare them? What’s the effective penetration of the app?

Closing thoughts

You can’t tech your way out of a policy or political problem. That said, I strongly agree with the what Apple, Google, and the Government of Canada have done here. If the policy decision is to continue to deploy these decentralized, anonymous exposure notification applications on a voluntary basis then we need to keep looking for ways to make them more effective and more compelling to download and use. Sharing more useful information with people could be a way to get more people to use the app and better inform public health authorities on what to do next.