The UK's Emergency Alert system is being testedon Sunday, with a message set to be sent to millions of devices across the country. A nationwide test of the alert will allow the government to check that the system is working as it's meant to, and that in the case of a real emergency, people will be successfully notified.

The system has been tested on a nationwide basis once before, in April 2023, and has since been deployed five times in real emergency scenarios, such as during Storm Darragh in December 2024.

When the emergency alert was tested in 2023, some mobile phones on the Three network did not receive the alert. After the test, the Government said it would resolve the issues so that everyone will receive the alert. This time around, the alert is set to go off at 3pm on Sunday, September 7, with a siren and vibration lasting around 10 seconds, or until the user switches the alert off.

However, you can opt out of the test.

To opt out, Apple iPhone users should go to settings, search for "Emergency Alerts", and turn off Severe & Emergency Alerts.

Android users can do the same by searching "Emergency Alerts" in settings and switching off Severe & Emergency Alerts.

Pat McFadden, Chancellor of the Duchy of Lancaster, said: "On Sunday, September 7, we will hold a UK-wide test of the Emergency Alerts system to ensure it works when we need it most.

"It is a vital tool for keeping the nation safe when lives are on the line – and every minute matters.

"We do not use the system often, but like the fire alarm in your home, it is always on standby should we need to act."

Motorists have been advised by National Highways not to reach for their phones, if the alarm goes off while driving.

The organisation stated: "Do not read or respond to an emergency alert while driving or riding."

National Highways' website adds: "Find somewhere safe and legal to stop before reading the message. If there's nowhere safe and legal to stop, and nobody else is in the vehicle to read the alert, you can listen to news on live radio to find out about the emergency. It's illegal to use a hand-held device while driving or riding."