The UK government will send an alert message to all 4G and 5G mobile phones at 3pm BST on Sunday 23 April 2023. It will be accompanied by a sound and vibration, and will occur on all devices, regardless of your network provider.

Don't be alarmed though (pun intended), it's a test of the UK's new Emergency Alerts system that is designed to warn people when there is an imminent risk to life. It's something that has already been implemented in other countries, such as the US and Canada, and has been used to warn phone owners in specific areas of disasters, including wildfires and flooding.

Why will my phone make a noise and can I stop it?

The government plans to send the message at the same time to all devices countrywide, although the technology can be used to target local areas too. It says all users will receive a text message, and phones will play a sound while vibrating for approximately 10 seconds. You do not need to do anything to stop it, it'll finish on its own, although you may need to swipe away the accompanying notification.

If you do want to avoid the Emergency Alert arriving at the allotted time, you can power down your phone completely for the period. However, there's no guarantee that it won't then arrive and occur after you switch it back on again.

Will all phones get the Emergency Alert?

The Emergency Alerts system targets all phones operating on 4G and 5G networks. That means legacy handsets that work on 3G will not receive the signal. In addition, if you don't have signal at the time of the alert, you won't get it either.

But, the government estimates that nearly 90 per cent of the UK's mobile phones will receive it and can therefore be further warned if there's a serious risk to life at a later date.

"Warning and informing the public at speed during times of crises can be vital," said the National Police Chief's Council lead, assistant chief constable Owen Weatherill.

"We look forward to further developing the use of the Emergency Alerts capability and how it can have real benefits for the public to protect and preserve life, as well as supporting policing’s wider response to critical incidents with partner agencies."

The police and other emergency services welcome the test - not least because public feedback can be used to refine the system for future use.

The timing of the test alert has been chosen to avoid the London Marathon, also taking place on Sunday 23 April.