All UK phones are about to light up with an emergency alert test, at exactly the same time. On Sunday, 23 April, at 3pm, phones will emit a loud, siren sound, vibrate and show a message on screen.

Remember that brief moment of icy fear that went down your spine every time you heard the start of an Emergency Broadcast ... as the alert played on TV and radio stations across the country ...

Once done, click Save. You can also update your existing eAlert phone number on this screen. When there is no eAlert phone number specified, the emergency alerts will be sent to the phone number of ...

The data within the tones tells equipment in any given TV or radio broadcaster who originated the emergency alert, what the alert is about, and the affected area, along with other metadata.