The government is rolling out a new Emergency Alerts system and a test alert will be sent out on Sunday 23rd April.
The alerts will be used to let you know about emergency situations (like severe flooding) through your mobile phone. However, the alert will be accompanied by a loud sound even if your phone is on silent. If you live with an abusive partner this could alert them to any secret or secondary phones that you may have.
Here's how you can turn alerts off, both on Android phones and on iPhones: Managing Emergency Alerts on your phone to stay safe if you're experiencing domestic abuse - YouTube
If you’re afraid of your partner call the free 24 hours a day National Domestic Abuse Helpline on 0808 2000 247, or live chat with them Monday-Friday, 3-10pm by going to nationaldahelpline.org.uk.