The UK’s Emergency Alerts system will undergo a nationwide test in September as part of efforts to strengthen the country’s preparedness for a range of disasters.

The system enables urgent messages to be broadcast to a defined area when there is an imminent risk to life, such as wildfires or severe flooding. Other countries such as the US and Canada already have such a system in place.

During the test, mobile phones will vibrate and make a loud siren sound for roughly 10 seconds, even if they are set to silent. A message will also appear on phone screens, making it clear the alert is only a test. There are approximately 87 million mobile phones in the UK.

The test, which will take place around 3pm BST on 7 September, is needed to ensure the system is functioning as planned, the Cabinet Office said.

Every 4G and 5G enabled device in the UK should receive an alert. However, when the system was first tested in April 2023, a small proportion of users did not receive it. Customers on the Three network appeared to be most affected, with a slew of reports that some users did not see or hear the alert. Since then, Three has merged with Vodafone, allowing customers of each firm to use the other’s broadcast towers.

Ahead of the national test, the government will be running a public information campaign to notify people that it is taking place. This includes communications targeted at vulnerable groups, such as victims of domestic abuse who may have devices that are kept secret from other members of their household. 

Pat McFadden, chancellor of the Duchy of Lancaster, said: “Emergency Alerts have the potential to save lives, allowing us to share essential information rapidly in emergency situations including extreme storms. Just like the fire alarm in your house, it’s important we test the system so that we know it will work if we need it.”

Since the first national test of the Emergency Alerts system in April 2023, five alerts have been sent, including during major storms when lives were at risk.

The largest ever use of the system saw approximately 4.5 million people in Scotland and Northern Ireland receive an alert during Storm Éowyn in January 2025 after a red weather warning was issued, meaning there was a risk to life. 

Approximately 3.5 million people across Wales and the south-west of England received an alert during Storm Darragh in December 2024. This storm killed two people. 

Other activations have included when an unexploded Second World War bomb was discovered in Plymouth, as well as during localised flash flooding in Cumbria and Leicestershire.

In January, the equivalent system in the US mistakenly sent a wildfire evacuation alert to the smartphone of every resident in Los Angeles County, a region with more than 9 million people.