Millions of mobile phones across the UK will emit a loud alarm and vibrate at 3pm on April 23 in a nationwide test of a new public alert system.
The system is intended to be used in life-threatening situations including flooding and wildfires.
The message will be received on 4G and 5G mobile phones, along with sound and vibration for up to ten seconds. But domestic violence campaigners have warned the test could put people in danger by revealing the location of secret phones hidden away by those at risk.
Phone users will be prompted to acknowledge the alert by swiping or clicking the message before being able to continue using their device.