Phones and tablets may unexpectedly make a loud sound like a siren when a new emergency alert system from the government is tested on Sunday April 23.

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

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

The alert will last around 10 seconds and you'll need to tap the message to clear it and carry on using the device.

An alert will include a phone number or a link to the GOV.UK website for more information.

People will not need to take any action after the test but in future it will warn you if there’s a danger to life near by.

It could also send alerts about severe flooding, fires or extreme weather.

They will only be sent by the emergency services, government departments, agencies and public bodies that deal with emergencies.

The government does not need to track you or know where you live or work to send you an alert.

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

Tests of the service have already taken place in East Suffolk and Reading.

Emergency alerts were used during wildfires in France and Greece last summer and in the US, Canada and Japan to alert people to earthquakes, flooding and wildfires.

They could eventually warn of ongoing terror attacks.