Jersey's Covid alert app, which has been downloaded onto nearly 40,000 phones, now works in England and Gibraltar.
The Jersey app can interact with the NHS Covid-19 and Beat Covid Gibraltar apps - alerting users if they've come into close contact with someone who has been diagnosed with coronavirus.
The Jersey app also works in, and with, the Scotland and Northern Ireland apps.
As long as Bluetooth remains on, the apps will be able to communicate with each other.
"Securing the compatibility between these apps will mean Islanders travelling all around the UK and to Gibraltar will be alerted via the COVID Alert app if they have been in close contact with someone who has the virus.
"The interoperability of the app allows any Islander who is identified as a direct contact to self-isolate quickly, reducing the risk of infecting others. While travel is currently restricted in England, the update to these apps will provide protection for those who need to travel for essential reasons such as work.
"It is an important step in protecting those that travel and preventing the spread of COVID-19." - Julian Blazeby, Director General for Justice and Home Affairs.
The Jersey app was launched nearly a month ago and sold as an extra layer of protection in keeping islanders safe.
People who get an alert will be told to phone the Contact Tracing Team for specific advice on what to do next.
"With so much of our travel to and from the UK it has always been a priority to make sure our own Covid Alert app would be interoperable with the NHS app and so it’s great news that we can finally announce that users of both, will be able to use their existing app regardless of which countries they are spending time in." - Tony Moretta, Digital Jersey CEO.