An emergency alert drill has been scheduled for next weekend, set to trigger a 10-second siren to more than 88 million mobile phones.
The alert will mark the second test of the national emergency alert system, after the initial test in 2023.
On Sunday September 7 at around 3pm, mobiles will emit a siren and vibrate for up to 10 seconds.
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Mobiles will have to be connected to 4G and 5G networks to receive the alert.
Users will also receive a message making clear that the alert is only a drill.
The Government has used the system to issue real warnings five times so far.
One of these occurred in January to make residents in Scotland and Northern Ireland aware of severe weather during Storm Eowyn.
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The emergency alert drill will take place on September 7 at around 3pm | GETTYAround 3.5 million people across Wales and South West England received an alert during Storm Darragh last December.
In February last year, around 50,000 phones were triggered to a warning of a 500kg unexploded Second World War bomb found in a Plymouth back garden.
Messages can also be sent to smaller areas to nail down the areas at risk.
In May 2024, some 15,000 phones were alerted during flooding in Cumbria.
In January of this year, around 10,000 phones received a warning during flooding in Leicestershire.
The system is designed for use during emergencies that are more likely to affect the UK.
Warnings would also be transmitted via television and radio.
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.
Around 3.5million people across Wales and the South West of England received an alert during Storm Darragh
| GETTY"It is a vital tool for keeping the nation safe when lives are on the line - and every minute matters.
"During Storm Darragh and Storm Eowyn, as millions faced dangerous extreme weather, I saw first-hand how effective it was at getting life-saving advice to at-risk communities in an instant.
"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.
"This test is part of our action plan to build resilience across the whole country and secure the nation under the Plan for Change - from the £1billion we're investing in a new network of National Biosecurity Centres to the £4.2billion we're investing to build a new generation of flood defences to protect local communities."