People in Cavan and Monaghan and other border areas could be affected by the new UK Emergency Alert System that takes place this Sunday.
Mobile phone customers on mobile phone networks based in Ireland will not receive the message.
However, anyone whose phone is roaming onto a tower operated by a UK network will get the message between 3pm and 4pm on Sunday afternoon.
A statement on the Department of the Environment website says a loud siren-like noise will play and the phone will use a distinct vibration. A message will appear on the home screen of the phone until it is acknowledged.
The UK Emergency Alerts System, which is operational across Britain and Northern Ireland, was launched on Sunday, 19 March.
The system enables the UK Government to send an 'alert' message to all mobile phones and devices (such as certain tablets) if there is an emergency (for example, an extreme weather event) where lives are endangered.
