neowin[.]net/news/uk-government-to-test-new-emergency-alert-system-on-sunday-afternoon-what-you-need-to-know/
gov[.]uk/alerts
What happens when you get an emergency alertYour mobile phone or tablet may:
make a loud siren-like sound, even if it’s set on silent
vibrate
read out the alertThe sound and vibration will last for about 10 seconds.
An alert will include a phone number or a link to the GOV.UK website for more information.
You’ll get alerts based on your current location - not where you live or work. You do not need to turn on location services to receive alerts.