The system was used to send alerts to 4.5 million phones in Scotland and Northern Ireland during Storm Eowyn in January 2025, and 3.5 million in England and Wales during Storm Darragh the previous month.
It was also used to aid the evacuation of more than 10,000 residents in Plymouth as an unexploded 500kg World War Two bomb was carefully removed and taken out to sea to be detonated after being uncovered.
Tracey Lee, chief executive of Plymouth City Council, said it had been an “invaluable tool” and provided residents with “clear information at a critical moment”.
While devices that are not connected to mobile data or wi-fi will still receive the alert, those that are switched off or in airplane mode will not.
Domestic abuse charities previously warned the system could endanger victims by potentially alerting an abuser to a hidden phone. The National Centre for Domestic Violence advised people with concealed phones to turn them off for the duration of the test.
The government stresses that emergency alerts should remain switched on, but has published a guide, external for domestic abuse victims on how to opt out.
The new test will also feature a version of the message in British Sign Language for deaf people.
