Millions of people across the UK will hear a loud alarm from their mobile phones, when a new 'Armageddon' alert is trialled within weeks.
The new UK-wide Emergency Alert system will be tested on Sunday, April 23 at 3pm, with Brits receiving a message to warn of danger to life nearby.
Messages will be sent out to 4G and 5G mobile phones, along with piercing sound and vibration for up to 10 seconds.
People don't need to do anything when the alert happens, simply swipe the message away or click 'OK' on their phone's home screen.
The test coincides with major events including the London Marathon and the 2pm Premier League matches between Bournemouth and West Ham, and Newcastle and Tottenham.
Similar alerts are already in use in countries like the US, Canada, the Netherlands and Japan, to warn of danger such as severe weather events.
In the UK, alerts are expected to be used in incidents such as wildfires or severe flooding.
Alex Woodman, Chief Fire Officer and Resilience Lead on the National Fire Chiefs Council, urged people to play their part in the test.
Writing in the Mirror, Mr Woodman said: "For 10 seconds, it may be inconvenient.
"But please forgive us for the intrusion, because the next time you hear it, your life and the life-saving actions of firefighters’ could depend on it."
The system will be used very rarely - only being sent where there is an immediate risk to people’s lives - so people may not receive an alert for months or years.
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Chancellor of the Duchy of Lancaster Oliver Dowden said: "Getting this system operational with the national test means we have another tool in our toolkit to keep the public safe in life-threatening emergencies.
"It could be the sound that saves your life."
People who do not wish to receive the alerts will be able to opt out in their device settings, but officials hope users will keep them turned on to keep themselves safe.
Domestic violence campaigners have warned that the alert could put people in danger by accidentally revealing secret phones to their abusive partner.
The National Centre for Domestic Violence (NCDV) warned people with hidden second mobile phones to turn off the alerts to avoid revealing the location of their devices.
NCDV's Sharon Bryan said: "Hidden second mobiles are an emergency lifeline for victims and survivors living under the constant threat of abuse, or worse.
"This siren test may unexpectedly reveal their presence to abusers - with disastrous consequences."
The Government said it has been actively engaging with organisations working with vulnerable women and girls to ensure they are not adversely affected by the introduction of emergency alerts.
