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Later this month, around 90% of Phones and tablets in the UK will unexpectedly make a loud sound like a siren.

The siren will be a test of a new emergency alert system from the government.

If it works, it may be used to warn people about floods or other life threatening situations in the future.

The government says it could one day be "the sound that saves your life".

When is the emergency alert system being tested?

The UK government's emergency alert system test will sound on Sunday 23 April at 3pm,

The sound may be different, depending on the device, but the government says it may make a loud siren sound (even if the phone or tablet is on silent).

It could also vibrate, or even read out a message automatically.

The alert will last around ten seconds and you'll need to swipe the message to clear it or hit "OK" and carry on using their device.

People who have their phones switched off will not receive the message.

The test had originally been planned for the early evening but was moved to avoid clashing with an FA Cup semi-final, which kicks off at 4.30pm.

The government was also keen to avoid a clash with the London Marathon, which starts at 9.30am on that Sunday.

What will the emergency alert system be used for?

The first time this alert happens it is just as a test so it's nothing to worry about, but in the future it could be letting you know about a real emergency.

The government says it could be used if you're somewhere where it may flood.

It could also be used for big fires, or extreme weather, like blizzards or big storms.

It could also be used during terror incidents or emergencies if the UK was under attack.

Only emergency services or the government will send warnings, so they say it's important to listen to them if you get one.

Can you turn off emergency alerts?

Although it's possible to turn the emergency alert system off, the government says there are lots of reasons to keep it on.

It says the warnings will only ever be sent if there's an "immediate risk to life," with a government minister adding "There's not going to be a general kind of spam system",

The government says the way they work means the system doesn't need to track you, or have any data sent back from you.

The alerts will be sent to every smart device near phone masts in the area where the emergency is.

But if you do want to turn them off, you can go into your phone's notification settings and switch off Emergency Alerts.

Do other countries have emergency alert systems?

All 4G and 5G Android and Apple phones are already fitted with emergency alert capability, as similar systems are in use in the United States, Canada, Japan and other countries around the world.

The government has said that the most common emergency in the UK is flooding, but other countries have already used it for situations including: