A loud alarm will go off on millions of mobile phones across the UK at 3pm today to test a new public alert system.

The noise, which will be no louder than a standard mobile ringtone, will last for about 10 seconds and is being sent to every 4G and 5G device across the UK.

Newly appointed deputy prime minister Oliver Dowden, the minister in charge of the system, said the UK public could “simply swipe away” the alert.

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However, he said in the future it might be the “sound that could save your life.”

The alert system will be used to warn the public if there is a danger to life nearby.

This could include extreme weather events, such as flash floods or wildfires, or during terror incidents or civil defence emergencies if the UK was under attack.

The test message will say: “This is a test of Emergency Alerts, a new UK government service that will warn you if there’s a life-threatening emergency nearby. In a real emergency, follow the instructions in the alert to keep yourself and others safe. Visit gov.uk/alerts for more information. This is a test. You do not need to take any action.”

People who do not wish to receive the alerts will be able to opt out in their device settings, and phones that are off or in airplane mode will not receive an alert.

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Drivers have been warned it will still be illegal to pick up their mobiles during the test

The government has timed the alert so it does not interfere with sporting events, such as the FA Cup semi-final and the London Marathon today.