Coronavirus: How the NHS contact-tracing app actually works – and what will happen if you receive an alert

A commuter uses his mobile phone inside the Gautrain after boarding at the Centurion Station in Centurion on May 4, 2020 (PHILL MAGAKOE/AFP via Getty Images)

The UK is finally testing an app that it hopes will prove one part of its fight against coronavirus.

The app – officially known as NHS COVID-19, and made for iOS and Android – is being trialled in the Isle of Wight and should be available for the rest of the country soon.

Its central function will be to use bluetooth technology to watch for connections to other phones that are also running the app, and build up a picture of who the owners of those phones may have been in contact with. If one person in that network says they have symptoms of covid-19, it will trigger an alert on other people's phones to encourage them to stay at home.

The government has suggested that the app will only serve one part of its plans for stopping the spread of the disease, along with more traditional and offline contact-tracing approaches. But it is nonetheless an important part, officials say, and people have been urged to download the app and help the country to fight the disease.

What is the app for?

A contact tracing app is one of the Government's next big areas of focus, part of a wider contact tracing effort, as it tries to find ways to end lockdown while preventing a possible second wave of the virus.

The app uses Bluetooth to keep an anonymous log of everyone you come into close contact with. When they - or indeed yourself - present symptoms of Covid-19, tell the app and it will then alert anyone that has been in close proximity.

"Something that is automated, that can work alongside traditional epidemiological contact tracing is potentially going to be of very great use to us," Professor Jonathan Van-Tam, deputy chief medical officer for England said.

How does the app work?

Once installed and set up, the app will run in the background, keeping a log of everyone you pass.

Users will need to provide the first part of their postcode and give the app permission to use Bluetooth, as well as its ability to receive notifications.

Bluetooth will need to be kept on, though the NHS has been clear that it uses a low power version of the technology that should not drain batteries.

When a person is feeling unwell, they need to send a report, stating whether they are experiencing a high temperature and a continuous cough, and when these symptoms started.

If it appears they might have the virus, the person will be told to book a test.

The information is then uploaded, along with the last 28 days of proximity events, and fed into a complex at-risk algorithm which crunches data such as distance, duration and symptoms.

It will only notify those deemed at risk to isolate for 14 days and ask them monitor their symptoms.

If the person's results come back as negative, those who came into contact with them will be told they are able to come out of isolation.

But should the result be positive, the person will be told to self-isolate for seven days, while those who came into contact with them continue self-isolating and book a test of their own if they have slightest symptom.

Will it work?

Contact tracing is really dependent on several crucial factors - though NHSX boss Matthew Gould has warned it will not be a "silver bullet".

"The app is exciting, but it's also not a silver bullet or a standalone solution, it's part of this wider strategy ... it has to be seen as part of this strategy alongside the expansion of testing and human contact tracing," he said.

The app is also voluntary, so its effectiveness will rely on the amount of people actually using it.

"Uptake is going to be important and so is the compliance with the app and regularly using it over a sustained period of time - and those are unknowns at the moment," Professor Van-Tam said.

"The market research we've done, I think, indicates for the UK that there's a fairly significant optimism that people will engage with something that is clearly about protecting the NHS."

Additional reporting by agencies