The app will send you a notification if it calculates that your phone has been in close contact with the phone of someone who has tested positive for coronavirus. The alert is anonymous and will not identify the person in any way.

A scientific calculation, using an “algorithm”, has been developed by NHS doctors and scientists to work out which app users are ‘close contacts’. ‘Close contact’ means that your phone has been within 2 metres for 15 minutes or more with the phone of someone who has tested positive for coronavirus. Read more about how the risk-scoring algorithm works.

Due to the data privacy-protecting features of the app, no personal data about you or any other app users can be accessed or shared. This means we cannot tell you who you've been in close contact with. Based on the Bluetooth signal of your phone, the length of time near to another device, and the level of infectiousness, the app is able to tell you if you've been close to someone who later tests positive, even if you do not know who that person is. For example, a stranger on a bus or someone you've stood close to in a long queue at the supermarket.

Following the app’s advice will help to break chains of transmission and will help to protect your loved ones and communities from coronavirus. The app’s self-isolation countdown timer can also help you keep track and link you to the latest government advice.

Read our guidance on what to do if you've been advised to self-isolate. If you have questions about how the advice in the app applies to you, or you're struggling with self-isolation, please call 111.