The UK government has announced a forthcoming nationwide test of its emergency alert system, designed to deliver critical warnings to mobile phones.
On September 7th at 15:00 BST, compatible smartphones will emit a 10-second siren sound and vibrate while displaying an emergency message, regardless of silent settings.
These alerts are intended for scenarios posing imminent threats to life, such as severe weather events or terrorist incidents.
While the system has seen regional deployments in recent years, a nationwide trial in 2023 encountered technical challenges, with some users receiving alerts prematurely or not at all.
Notably, a significant portion of Three network subscribers did not receive the alert, alongside users on other providers, while some received multiple notifications. Government data later revealed that the initial alert failed to reach approximately 7% of compatible devices.
The Cabinet Office stated that a thorough review of the previous issues would be conducted and addressed before a subsequent test.
The September test aims to validate the system’s functionality and familiarize the public with the alerts, aligning with practices in countries like the United States and Japan.
The alert will be delivered to smartphones connected to 4G or 5G networks, representing a subset of the UK’s estimated 87 million mobile phones. Older devices using 2G or 3G networks will not receive the test message.
Cabinet Office minister Pat McFadden emphasized the importance of the test, stating: “Just like the fire alarm in your house, it’s important we test the system so that we know it will work if we need it.”
The system has been previously utilized in regional emergencies, including 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 prior month.
It also played a role in the evacuation of over 10,000 Plymouth residents during the careful removal and detonation at sea of an unexploded 500kg World War Two bomb.
Plymouth City Council Chief Executive Tracey Lee described the system as an “invaluable tool” that provided residents with “clear information at a critical moment.”
While devices without mobile data or Wi-Fi will still receive the alert, those that are powered off or in airplane mode will not.
Domestic abuse charities have raised concerns about the potential risks to victims, as the alert could expose hidden phones to abusers. The National Centre for Domestic Violence has advised individuals with concealed phones to switch them off during the test.
The government maintains that keeping emergency alerts enabled is crucial but has published guidance for domestic abuse victims on opting out.
The upcoming test will also include a version of the message in British Sign Language to ensure accessibility for deaf individuals.