The Irish company behind Ireland's Covid-19 tracker app has launched a similar service in the US state of Pennsylvania.
The technology is now being used in Ireland, Northern Ireland, Gibraltar, Scotland and will be launched in more US states over the coming weeks.
Yesterday, Jersey, the largest of the Channel Islands, announced it would also be using NearForm's app.
The US service will allow for interoperability and exposure notifications across state lines that also have exposure notification apps and use the same Bluetooth technology.
Cian Ó Maidín, the CEO of NearForm, said the state of Pennsylvania was using technology that has been peer-reviewed and rolled out successfully in Ireland and parts of the UK.
"The COVID Alert PA app empowers the people of Pennsylvania to join the fight against the spread of COVID-19, and helps people protect themselves and their loved ones." Mr O Maidín said.