Amid calls for a national contact tracing app, experts have warned we shouldn't be placing all of our hopes on a smartphone solution when it comes to tracking down people potentially exposed to Covid-19.

Under alert level 2, hospitality and retail businesses are legally required to keep records of customers coming into their premises, sending companies toward various tracing tech in the absence of an official app.

But Victoria University computer scientist Simon McCallum has cautioned digital solutions might not be effective as we think.

"Tracing tech is great for some aspects of tracing, but humans who can ask questions and hear answers can often pick if someone is certain of information or if there is uncertainty in the answer," he said.

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"Technology is generally not as good at dealing with uncertainty."

There were questions around the level of false positives that could be generated by contact tracing technology – as well as associated false negatives.

"False positives could occur when we mark someone as being close who is actually on the other side of a wall," he said.

"Our systems for locating people in an indoor space accurately rely upon additional beacons placed in known spots or using extra information such as the layout of the building.

"We work with these issues with intrusion detection systems all the time and operator overload when the system over identifies people is a real concern."

McCallum suggested simpler techniques, like QR barcode reading, might actually be more fit for purpose as people would have to actively check-in at a cafe or other place would occur.

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"There are even potential non-digital solutions which involve random numbers generated by the Ministry of Health and printed on pieces of paper," he said.

"These can be left with a business or person as a way of contacting people without having to give away your phone number to everyone you meet."

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Other experts have pointed out some further potentially thorny issues.

Ian Welch, an asssociate professor at Victoria University, said businesses refusing entry to certain people who couldn't be tech-traced risked creating issues around equality and discrimination.

Some people simply couldn't afford phones; others might have problems with software storage, or not being able to support the necessary Bluetooth features.

And then there were issues around how people were officially notified by tracers that they may have been exposed.

"Notifications should be informative and helpful without causing panic, or compromising privacy of positive cases," Victoria University's Dr Jennifer Ferreira said.

"Government messaging has aimed to reduce panic reactions and focus on preparedness.

"This serves as a helpful design guideline in any technology design process.

"People are already in a heightened state of anxiety and we should not contribute to worsening the situation."

The Australian Government say it's vital to know quickly if people have come in contact with someone who has tested positive for coronavirus. Video / Australian Government

Ferreira said there were a multitude of privacy issues with the notification process, specifically about how to disclose information to users of the tracing technology around when and how contact occurred.

Google and Apple had not gone as far as detailing that process in their approach, which she thought a potentially large oversight, given their own admission of the number of false positives.

"The notification process may be better handled outside an app by health professionals.

"The issue of who should be informing people about being positive reminds me of the debate around the wisdom of home HIV testing, another situation where the advice is to test early and test often."

How Maori took part in tech tracing was another big consideration.

"Historically, Maori have suffered at the hands of previous government policies, which has over-time created a level of mistrust," Victoria University senior lecturer Kevin Shedlock said.

Building contact tracing applications from a kaupapa perspective, he argued, should consider the available expertise within Maori communities during the tech's development.

"Adopting kaupapa Māori methods during the construction of any technology such as mobile tracing applications is also about having an understanding of the relationships and accountabilities associated with being in a trusted Māori community," he explained.

"Kaupapa Māori systems ask different questions, align with different practices and prioritise tasks differently during the construction of technology. Such practices and priorities must continue to be preserved."

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The Government has tried to overcome many of the headaches of contact tracing by adopting most of the recommendations of a review by Otago University epidemiologist Dr Ayesha Verrall.

Public health units could now trace up to 185 cases each day, while the newly-formed National Close Contact Service could make up to 10,000 close contact calls in a day.

But ultimately, McCallum believed speed was more important than capacity at this stage.

"We have the capacity but with the spread of Covid-19, we have to get to people before the infection gets ahead of tracing," he said.

"With the exponential growth rate if you can track quickly you do not need as much capacity."

Covid19.govt.nz: The Government's official Covid-19 advisory website