Almost everyone in the UK with a mobile phone will be part of a nationwide test on St George's Day as the government sends out a test emergency alert.
The siren and message will appear on people's screens on Sunday, April 23, with their phones locked until they acknowledge the warning.
A video of how the alert and what it will sound like on an iPhone has been released by the government as they hope everyone will take part.
People are able to turn off the alerts within their phones settings but it is hoped the benefit of being warned about a life-threatening situation will mean most keep them on.
The alerts have been used in parts of Europe, the US, Canada and Japan and alert people to earthquakes, flooding and wildfires, and could eventually warn of ongoing terror attacks.
Officials have acknowledged however that much more information about how the alerts system operates in the UK would be needed before that could happen in response to a fast-moving attack.
The believe the scheme will be able to get a message to 90% of mobile users within the relevant area in an emergency.
Alerts will only ever come from the Government or emergency services, and after this nationwide test they will include the details of the area affected, and provide instructions about how best to respond.
People will not need to take any action after the test on Sunday, April 23 but will need to hit ok for their phone to be functional again.
The Cabinet Office said the alerts are secure, free to receive, and one-way, insisting they do not reveal anyone’s location or collect personal data.
Tests of the service have already taken place in East Suffolk and Reading.
Chancellor of the Duchy of Lancaster Oliver Dowden said: "We are strengthening our national resilience with a new emergency alerts system, to deal with a wide range of threats - from flooding to wildfires.
"It will revolutionise our ability to warn and inform people who are in immediate danger, and help us keep people safe."
He added: "As we've seen in the US and elsewhere, the buzz of a phone can save a life."
People who do not wish to receive the alerts will be able to opt out in their device settings, but officials hope the life-saving potential of the messages means that users will keep them on.
National Fire Chiefs Council chairman Mark Hardingham said: "Together with every fire and rescue service in the country, I'm looking forward to having emergency alerts available to help us to do our jobs and to help communities in the event of emergencies.
"We've seen this type of system in action elsewhere across the world and we look forward to having the facility here in the UK – by working together with fire services and partners, we want this system to help us to help you be as safe as you can if a crisis does hit."
The Environment Agency's executive director for flood and coastal erosion risk management, Caroline Douglas added: "Being able to communicate warnings in a timely and accurate manner during incidents is really important to help people take action to protect themselves, their families, and their neighbours."
