It's being rolled out across England and Wales today, but there have been questions about its effectiveness.
The latest version of the app has been in testing among residents on the Isle of Wight and in the London borough of Newham since mid-August, after the first was marred by technical issues and eventually scrapped.
Though the Bluetooth-reliant technology was initially described as the “best possible way to help the NHS” by Transport Secretary Grant Shapps in May, results from other countries already using apps have been mixed.
As the software is voluntary, its success will also depend heavily on how many people choose to download and use it.
Professor Christophe Fraser, scientific adviser to the Test and Trace Programme, said: “Our Oxford University research team analysis has shown the potential to meaningfully reduce the number of coronavirus cases, hospitalisations and deaths across the population from as little as 15% of the whole population downloading the app and following the guidance to self-isolate.
“This means each one of us can make a difference to help stop the spread of infection, save lives and help protect our loved ones.”
It comes at a critical time for the UK, with confirmed cases of Covid-19 on the rise daily.
The app uses an Apple and Google-developed system, using Bluetooth to keep an anonymous log of people a user has been close to.
If a person develops symptoms, they can check with the app and book a test.
Should it come back positive, close contacts will be informed to self-isolate by an app notification.
A QR code scanning feature is available, allowing people to check-in to venues they visit and easily share their contact details for human tracing efforts.