Millions of people will receive a message on their mobile phones at 3pm on Sunday as part of a UK-wide test of an emergency alarm system.
The alarm will appear on mobile phones and tablets, accompanied by a loud warning sound and vibration.
The Government has defended conducting the test and insists there's been sufficient information to brace the public to avoid causing unnecessary concern.
The system will in future be used to warn the public about severe flooding, fires and extreme weather, with the Government saying the system will be used sparingly.