A Covid-19 tracing software tool has appeared in the settings of both Android phones and iPhones as part of an update of their operating systems.
The "exposure notification" tool is switched off by default, and is not a tracing app itself.
It enables an app to run in the background while still using Bluetooth.
This lets the app measure the distance between two handsets - and then alert the phone owner if someone near them later tests positive for Covid-19.

To help understand whether you've been exposed to someone who reports having COVID-19, you can turn on Exposure Notifications. If you change your mind, you can turn it off.