Time and date revealed when millions of mobile phones will go off at once

Millions of mobile phones will sound in unison across the United Kingdom when an emergency alert system is tested next week. The second ever national alert test will take place at around 3pm on Sunday September 7, in what the Government calls "one of the largest public safety exercises of its kind".

Phones will vibrate and emit a siren-like tone for ten seconds, with a test message appearing on screens to make clear the alert is only a drill. Planned for Sunday afternoon, the timing has been carefully chosen by emergency planners in COBR, to minimise disruption to work and school routines.

Pat McFadden, Chancellor of the Duchy of Lancaster, said: "Next Sunday will be one of the UK's largest public safety exercises in history, as we ensure the Emergency Alerts system is ready to help keep the country safe.

"The test alert will be issued by COBR, the government's emergency planning team whose work usually takes place behind the scenes.

"Emergency Alerts have the power to save lives. In real life emergencies, it's vital to rapidly share warnings and advice, which is why we keep the system on standby 24/7."

COBR brings together ministers, senior officials and expert planners to coordinate the national response during major incidents.

Since the Emergency Alerts system was launched in April 2023, it has been used five times to warn of life-threatening danger, including during Storm Éowyn in January 2025, when 4.5 million people across Scotland and Northern Ireland received an urgent warning of extreme conditions.

The system has also proved invaluable in local emergencies. In Plymouth, more than 10,000 residents were evacuated in hours after an unexploded Second World War bomb was discovered.

Only 4G and 5G enabled phones and tablets will receive the alert next Sunday. Devices also need to be turned on and within range of a mobile phone mast.

The message will say: "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."

It follows the publication of the government's Resilience Action Plan, which sets out plans for a £1 billion new network of National Biosecurity Centres and £4.2 billion to strengthen flood defences.