The government has urged people to “keep their cool” when the national system for sending emergency alerts to mobile phones in the UK is tested on Sunday.
At 15:00 BST, compatible phones will vibrate and make a siren sound for 10 seconds, even if set to silent. They will also display a message explaining that a test is taking place.
The alerts are intended for situations in which there is an imminent danger to life, such as extreme weather events or during a terror attack.
Pat McFadden, the newly-appointed work and pensions secretary, said the test is “to make sure the system works well when we need it most”.
It is just the second time the system has been tested nationwide, and comes more than two years after the first revealed a number of technical issues.
Many people reported the alert went off one minute earlier or later than planned. Some said they did not receive the alert at all.
McFadden, who until Friday’s government re-shuffle served as a senior Cabinet Office minister, said: “I know Brits will keep their cool when phones across the UK make a siren-like noise… It’s important to remember this is only a test, just like the fire drills we all do in our schools and workplaces.”
He added: “We’re carrying out the test to make sure the system works well when we need it most, and afterwards, we’ll work with mobile network operators to assess performance.
“The test takes just 10 seconds, but it helps us keep the country safe 24 hours a day, 365 days a year,” he said.
It will see compatible phones – the vast majority of those currently in use – vibrate and make a siren sound for 10 seconds, while displaying a message.
The text of the message will read: “This is a test of Emergency Alerts, a UK government service that will warn you if there’s a life-threatening emergency nearby.
“You do not need to take any action. In a real emergency, follow the instructions in the alert to keep yourself and others safe.”
Phones that are switched off or in airplane mode will not get the alert.
The system has been deployed regionally five times in the past few years.
Around 4.5 million phones in Scotland and Northern Ireland were sent an alert during Storm Eowyn in January. The previous month, around 3.5 million were sent alerts in England and Wales during Storm Darragh.
The system was used last February to aid the evacuation of more than 10,000 residents in Plymouth, after a 500kg unexploded World War Two bomb was discovered.
Messages have also been targeted to relatively small areas to pinpoint those at risk, including during flooding in Cumbria in May 2024, and for similar weather conditions in Leicestershire in January.
Domestic abuse charities previously warned the system could endanger victims by potentially alerting an abuser to a hidden phone. The National Centre for Domestic Violence advised people with concealed phones to turn them off for the duration of the test.
The government has stressed that emergency alerts should remain switched on, but has published a guide for domestic abuse victims on how to opt out.
