The NHS has introduced a test and trace schemes to help the UK lift lockdown measures and stop the spread of coronavirus.
Thousands of contact tracers have been recruited to notify people – by email, text or by phone – if they’ve come into contact with someone with Covid-19.
Wales launched their system on 1 June and England, Scotland and Northern Ireland have systems up and running.
The UK’s test and trace app is currently being trialled on the Isle of Wight but isn’t ready yet to be rolled out elsewhere.
BBC Health and Science correspondent, Laura Foster, explains what is meant by track and trace, how it works and how it can keep the R number low.
Video by Laura Foster, Terry Saunders, Tobias Chapple and Ameer Ahmed