The functionality is provided by the Google and Apple Exposure Notification Framework, which most Android devices and iPhones already support. The Ministry of Health says people should continue scanning in with the QR codes, as keeping a digital diary is still important in staying ahead of the fight against COVID-19.
This is a companion discussion topic for the original entry at https://www.sciencemediacentre.co.nz/2020/12/09/bluetooth-comes-to-covid-tracer-app-expert-reaction/