A downward trend in the number of Kiwis using the NZ Covid Tracer app has prompted a fresh appeal for people to keep doing their bit against Covid-19.

Dr Andrew Chen, a researcher at University of Auckland-based Koi Tū: The Centre for Informed Futures, has been observing daily numbers of QR code scans over the latest outbreak.

The day Auckland's community outbreak was announced on August 11, there were some 30,659 scans.

The following Tuesday, with the city under lockdown and the rest of New Zealand at alert level 2, more than 1.1 million scans recorded.

Numbers followed a general upward trend over the next few weeks, reaching 1.7 million the week Auckland dropped down to level 2.5, and hitting a peak of 2,506,745 on September 5.

By September 14, the total had fallen to 1.6 million, before sliding further to 1.5 million on September 20 and 1,049,949 yesterday.

While there are now 2.2 million registered users of the app – with more than 64 million poster scans and three million manual data entries to date – Chen was worried people were becoming complacent again.

"I think what we are seeing is, initially people quickly got on board and started using the app to scan QR codes when it became mandatory, but now they might not necessarily see a direct benefit in scanning."

He said regularly using the app was critical in being able to give contact tracing services a 14-day log of personal movement.

"It's about protecting yourself, because the Ministry of Health can let you know more quickly and easily if you've been exposed to Covid-19."

Just as importantly, it allowed tracers to track down others who might have been exposed to the virus, and having a log also meant they could match up cases, and potential transmission, where check-ins overlapped.

Modeller Professor Shaun Hendy, of Te Punaha Matatini, echoed Chen's message to the public.

"We've been through this second outbreak and it's perfectly understandable that people are starting to relax - but it's important we keep up those scans," he said.

"It's the sort of thing that could prove essential if we have another outbreak, or if this one kicks off again. The more of us who are using it, the better."