Might be worth adding a reminder to your calendar (to reduce being startled):
"The national system for sending emergency alerts to mobile phones in the UK will be tested again this September, the government has said.
It will see compatible phones vibrate and make a siren sound for 10 seconds while displaying a message at 15:00 BST on 7 September, even if they are set to silent."
For those who wish to not receive this alert, it will not work if the phone is turned off. Also users may turn off alerts on their phone - on my android one it's in settings, Apps & notifications, Advanced, Emergency Alerts.
