News that Australia and New Zealand will form a safe travel zone as soon as possible was a welcome development for exports, tourism and divided families.
But quarantine-free travel between the two countries also narrows options for a tracing app.
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A tracing app will be an essential tool as people move around within the transtasman bubble.
On one level, it would be logical to use a slightly modified version of the Australian government's COVIDSafe app, which is already up and running and downloaded by millions of Aussies.
Adoption is now close to the target of 40 per cent, and could rise with employer group pressure on the Morrison government to make it mandatory for workers to install the app as a condition of returning to an office or factory.
But COVIDSafe is far from perfect. It's based on the TraceTogether app developed by the Singapore Government, which was good enough to open-source its code (make it freely available for others to adopt and adapt).
COVIDSafe is pretty clever. It uses your phone's Bluetooth function to record when you spend at least 15 minutes within 1.5m of someone (as long as they're also using the app). It can then alert you if you've been near someone who is infected, without revealing their name.
Australia's app is voluntary, let's you register with a pseudonym and wipes data after two weeks - all features that are good for privacy (if not hardcore, Wuhan-style enforcement).
Analysis: What's wrong with Australia's tracing app - and an NZ firm's alternative
There are, however, a couple of key usability drawbacks. iPhone users have to remember to start it, then leave it running. And many phones, both iPhone and Android, automatically switch off Bluetooth when power is low, or when privacy settings are tweaked. There's also been confusion over whether COVIDSafe's failure to work on iPhones in lockscreen mode is a bug or an inherent limitation.
Would you install a govt contact tracing app on your phone? (Assuming there’s a pledge to only use it for Covid 19-related tracing and delete all data after the outbreak)— Chris Keall (@ChrisKeall) April 27, 2020
And even when Singapore's infection rate was remarkably low, COVIDSafe's close cousin TraceTogether was never looking perfect.
Total adoption was around one-in-five as of late April - a surprisingly low figure for Singapore's compliant, tech-savvy population.
Jonathan Brewer - a Kiwi telco consultant locked down in the city-state - told the Herald beyond TraceTogether's usability limitations, many people in the at-risk over-65s either had "feature phones" (cheaper or older phones than can't download apps) or did own a smartphone but never downloaded ups.
Migrants were another at-risk group under-represented in TraceTogether adoption.
And now that the country's cases have spiked sharply n the past 10 days, TraceTogether (and by extension Australia's COVIDSafe) looks outright ineffective.
There are some interesting alternatives. NZ company Integrated Integrity says it has a production-ready solution that would mate Bluetooth tracking with scanning QR codes when you enter popular locations.
And Apple and Google have combined forces to create a Bluetooth tracing app that would work for both iOS (Apple) and Android phones (almost all the rest) all the time - with no requirement for the user to switch it on or wake it up.
We won't see the final Apple and Google spec until later this month, but previews are promising with full encryption and a pledge not to commercialise data (Google, of course, usually lives to exploit our data for ad words, but Apple has different DNA with its focus on hardware, software and services revenue and has often rubbed authorities up the wrong way with its insistence on strict user privacy provisions).
The Apple-Google solution won't be perfect, of course, but the early signs are that it would be worth a look ... or at least it would be if our larger sibling hadn't effectively already chosen for us.
Even before plans for a transtasman bubble were formalised, our PM was name-checking TraceTogether (which can now be thought of in the same breath as its close offspring COVIDSafe).
Now, it seems a dead cert that NZ will base its tracing app on the Singapore government's effort.