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Some people in East Suffolk might hear an unusual and loud alert coming from their phone today (25 May).
In real terms, what it will mean today is that random phones are going to make an unexpectedly loud noise.
If it happens to you, at least you'll know what it was, and can get on with your day.
However, if you hear it again at some point in the future, it might be worth checking your phone to see what's going on.
Systems such as this one already exist in the USA, Canada, South Korea, Japan, New Zealand, and the Netherlands, and are used to alert the public when there is something they should seriously know about.
That can be severe flooding, fires, explosions, terrorist incidents and public health emergencies.
Let's hope it never comes to that, but those are the sorts of times you might hear this alert again.
The sound is to be tested in East Suffolk today between 1.00pm and 2.00pm, Metro reports.
Selected people will hear a 'loud tone and vibration that is hard to ignore and conveys urgency' from their phones and tablets, even if they're on silent.
The device may also vibrate, or even read out the alert.
If you're one of those people, you don't need to do anything upon hearing the sound, the test doesn't require a response.
Just try not to jump out of your skin, you've been warned now.
The decision to take on this kind of system has come a little bit too late for the Covid-19 pandemic, and the government has been relying so far on mobile operators to get messages out to the population.
Officials claim the system doesn't put any additional pressure on telecoms networks and won't share any personal details such as phone numbers.
If today's trial run is successful, there are plans to roll out the emergency alert system across the rest of the UK later this year.
The Paymaster General Penny Mordaunt said: "The Emergency Alerts service will be a vital tool in helping us to better respond to emergencies, both nationally and locally.
"The concept was used to good effect during the pandemic when we asked people, via text message, to stay at home to protect the NHS and save lives.
"This new system builds on that capability and will allow us to more quickly and effectively get life-saving messages to people across the UK."
Well, let's just hope that we never have to hear it in action.
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