England and Wales have launched a contact tracing app, which tells people to self-isolate if their phone detects they were near someone who tested positive for Covid-19.
The app was downloaded 14 million times in its first week.
Refusing to self-isolate when told to is now illegal in England, with fines of up to £10,000.
How do I download the app?
You can download the app on a smartphone - but not on tablets, smartwatches or other devices.
Your phone must have Android 6.0 (released in 2015) or iOS 13.5 (released in May 2020) and Bluetooth 4.0 or higher. That excludes the iPhone 6 and older versions of Apple's handsets. Some more recent Huawei phones will not load the app either.
What can the app do?
The app can detect when a fellow app user is nearby.
When two phones running the app are near each other, they will make contact through Bluetooth.
If they are close for a long enough time, and one of the two owners later shares a positive coronavirus test via the app, then the other will receive an alert.
You can also use the app to check in at venues - for instance, shops, bars, restaurants or places of worship.
Hospitality venues such as pubs and restaurants will be asked to display posters with a QR code, which app users will be able to scan.
The posters will also go up in communal areas of community buildings such as universities, hospitals and libraries.
Used alongside manual contact tracing, the app will help identify close contacts of a user who tests positive, or visitors to a premises that has suffered an outbreak.
How has contact tracing been carried out until now?
They are asked to log on to the NHS Test and Trace website and give personal information, including:
- name, date of birth and postcode
- who they live with
- places they visited recently
- names and contact details of people they have recently been in close contact with
Close contacts are:
- people you've spent 15 minutes or more with - at a distance of less than 2m (6ft)
- sexual partners, household members or people you have had face-to-face conversations with - at a distance of less than 1m
Contact must have taken place within a nine-day period, starting 48 hours before symptoms appeared.
No-one who is then contacted will be told your identity.
What happens to people who are then contacted?
If you are approached because one of your contacts has tested positive, you must stay at home for 14 days from your last point of contact with them.
You must self-isolate, even if you don't have symptoms.
Others in your household won't have to self-isolate unless they also develop symptoms, but must take extra care around you regarding social distancing and hand washing.
How is the tracing scheme going?
The prime minister claimed the UK's test and trace system would be "world-beating". But it has encountered several problems since its launch in May.
Of the people referred to the contact tracing system between 17 and 23 September, 71.3% were reached and asked for a list of their contacts, a fall of almost 10% on a week earlier.
Of those contacts, 71.6% were reached and asked to self-isolate, slightly more than the week before.
Scientists have suggested that the scheme needs to reach a much higher proportion of the population than this to be effective.
Sage, which advises the government, has said that at least 80% of contacts would need to isolate for it to work properly.
The mobile app was meant to launch in mid-May and form a key component of the UK's tracing strategy. But the original attempt, which used a ''centralised'' approach to storing data, had to be abandoned.
An NHS Test and Trace call does not always mean a pub or restaurant must close. It depends on the circumstances and when the infected person visited.