A new Covid-19 tracking feature has appeared on Androids and iPhones – but it’s not a contact-tracing app.

The new settings are part of an update to the operating systems, which will enable an app to run in the background.

The “exposure notification” allows contact-tracing apps to send a notification if you’ve likely been exposed to Covid-19.

The tool is switched off by default and requires a user to opt-in to the system. Once opted-in the system will generate a random ID for an individual’s device, which will be exchanged between devices using Bluetooth to monitor the spread of the virus.

The exposure notification system also allows an app to measure the distance and duration between two devices, alerting users if someone they’ve been near later tests positive.

The update is not a contact-tracing app but will be needed for an app to work on a device.

On Android it can be found in the Google section of the settings menu, and on iPhone it is found in the health subsection of the settings app.

The update comes after the government abandoned its centralised contact-tracing app in favour of a decentralised version from Apple and Google.

Instead NHSX will be working with the tech giants to develop a companion app that supports the “end-to-end” NHS test and trace service.

Field tests on both versions of the technology revealed problems with the NHSX and Apple and Google system.

The NHSX version was able to register about 75% of nearby Android devices, but just 4% of iPhones. The Apple and Google model was more accurate, logging 99% of Android devices and iPhones, but had difficulty measuring the distance between users’ devices.

In a joint statement Baroness Dido Harding, chair of the test and trace service, and NHSX CEO Matthew Gould, said their ambition was to develop an app that would “enable anyone with a smartphone to engage with every aspect of the NHS test and trace service”.

The test and trace service was launched on 28 May without the app, despite it being touted as a major part of the system earlier in the year.

A trial of the NHS contact-tracing app began on the Isle of Wight in the first week of May, but not date for a wider roll-out of the tool has been confirmed.

NHSX is continuing to work on developing an app but it is not know if it will be in place before the winter.