A siren-like alert will be sent to smartphone users across the UK to test a new government public warning system.
It allows the government and emergency services to send urgent messages warning the public of life-threatening situations like flooding or wildfires.
The test is expected to take place in the early evening of 23 April.
Phone users will have to acknowledge the alert before they can use other features on their devices.
A message will appear on the home screens of people’s devices during the test, with vibration and a loud warning sound that will ring for about 10 seconds, even if the phone is set to silent.
The system – which became operational on Sunday – is being modelled on similar schemes used in the US, Canada, Japan and The Netherlands. Emergency alerts work on all 4G and 5G phone networks and will not include older “non-smart” phones, the government said.