The loud, jarring sound that interrupted Sunday afternoon for millions across the UK was no cause for panic—it was just a test. At 3pm on 7 September 2025, the government conducted its second nationwide test of the Emergency Alerts system, sending notifications to compatible mobile phones throughout the country. The system, which has already saved lives during severe weather events, represents a crucial evolution in how authorities communicate with the public during emergencies.
The UK Emergency Alert system is a service that sends urgent warnings to mobile phones when there is an immediate risk to life, health, or property. These alerts are used for major incidents such as severe flooding, extreme weather, and terror attacks.
How the System Works
Technology lies at the heart of this potentially life-saving service. The system uses “Cell Broadcast” technology, which broadcasts messages to all compatible phones within range of specific mobile phone masts. An alert triggers a loud, siren-like sound and vibration, and displays a text message on screens that users must acknowledge to dismiss. The message provides information on the nature of the emergency and any necessary actions to take.
Compatibility is straightforward—most 4G and 5G smartphones will receive alerts. Users do not need to be connected to Wi-Fi or have mobile data enabled. However, phones that are switched off or in aeroplane mode will not receive an alert.
Real-world use has proven the system’s value. The system has been used for events like Storm Eowyn in January 2025 and to coordinate an evacuation in Plymouth after the discovery of an unexploded WWII bomb in February 2024.
Receiving Alerts
The process is entirely automatic—users do not need to sign up to receive alerts. Privacy concerns are addressed through the system’s design, as no personal data, such as location, phone number, or identity, is collected.
Before tests, domestic abuse charities have highlighted risks to people with concealed phones. The government has published guidance on how to opt out for these vulnerable individuals.
How to Opt Out
While the government advises against it, users can choose to opt out of non-critical alerts. On an iPhone, settings can be found under Settings > Notifications > Emergency Alerts. On an Android phone, users can search settings for “emergency alerts” to manage notification settings.
When Real Emergencies Strike
Since the system launched in March 2023, it has been deployed five times during genuine emergencies. Each activation has reached millions of people, providing critical information when seconds matter.
Storm Eowyn stands as perhaps the most significant test of the system to date. On 23 January 2025, approximately 4.5 million people in Scotland and Northern Ireland received an emergency alert warning them about the approaching storm. The Met Office had issued a rare red weather warning, predicting wind gusts of up to 100mph in coastal areas. The alert, sent at around 6pm the evening before the storm hit, urged people to stay indoors and avoid unnecessary travel.
The storm proved to be the most powerful to hit the UK in over a decade, with fifteen weather stations recording new gust records for January. Schools closed, transport networks shut down, and hundreds of thousands were left without power. British Red Cross emergency response teams supported more than 1,000 people across affected regions, conducting door-to-door welfare checks and providing remote telephone support to vulnerable individuals.
The Plymouth Bomb Scare
The system’s versatility was demonstrated during a different type of emergency in February 2024. When a 500kg unexploded German bomb from World War Two was discovered in a back garden in Plymouth’s Keyham area, authorities faced a massive evacuation challenge. The emergency alert system proved invaluable in coordinating the response.
More than 10,000 residents needed to evacuate from within a 300-metre radius of the bomb’s location and along its transport route. The alert sent to mobile phones on 23 February 2024 provided specific instructions about the cordon area and timing. It told residents they must leave by 2pm for their safety, as the bomb would be transported by military convoy to Torpoint Ferry slipway for disposal at sea.
The operation involved more than 100 personnel from the British Army and Royal Navy, including around 30 of the Armed Forces’ most experienced bomb disposal experts. During a press conference at the cordon, the emergency alert rang out on journalists’ mobile devices, demonstrating the system’s reach. Most affected residents were able to return home by 5pm that day.
Technology Behind the Alerts
Cell Broadcast technology represents a significant advancement over traditional warning methods. Unlike SMS messages, which are sent to individual phone numbers, Cell Broadcast sends messages to all compatible devices within a specific geographic area. This means alerts can reach people rapidly without requiring their personal information.
The system works with mobile phone masts to define alert areas, which can be as small as a local community or as wide as the entire country. When an alert is issued, all 4G and 5G devices within range receive the message simultaneously. The technology ensures the alert will sound even if phones are set to silent mode, though users driving are advised not to pick up their phones until safely stopped.
Around 95 per cent of the UK population has access to 4G or 5G networks, meaning the vast majority of the country’s approximately 87 million mobile phones can receive alerts. Older devices limited to 2G or 3G networks will not receive messages.
The September Test Results
The 7 September 2025 test marked only the second nationwide trial of the system since its launch. Pat McFadden, Secretary of State for Work and Pensions, emphasised the importance of regular testing to ensure the system functions effectively when needed most. The test occurred more than two years after the first national trial in April 2023, which revealed several technical difficulties.
During the 2023 test, numerous users reported receiving the alert either earlier or later than scheduled, whilst some did not receive it at all. Many users on the Three mobile network experienced problems, though some customers on O2 and Vodafone also reported difficulties. The government later confirmed that approximately 7 per cent of compatible devices failed to receive the alert.
Oliver Dowden, who was Deputy Prime Minister at the time, told Parliament he had initiated the 2023 alert at 14:59 BST rather than 15:00 to minimise potential disruption to events starting at 3pm. The alert remained active until 15:21 BST.
Addressing Domestic Abuse Concerns
The emergency alert system has raised important concerns within domestic abuse charities. Victims who maintain hidden phones as lifelines to support services face potential danger if an alert reveals their concealed device.
Naomi Long, Justice Minister, acknowledged these risks before the September test. She noted that perpetrators often control victims’ communication, monitoring phone use to isolate them from family, friends, and support networks. For some victims, a secret phone represents their only means of contacting help in an emergency.
Women’s Aid NI warned that the test could induce distress and fear among women in abusive relationships. The charity emphasised that for those in controlling relationships, the anxiety of their abuser discovering a concealed phone can be overwhelming and may present a serious danger to their safety.
Emma Pickering from Refuge stated that whilst technology itself is not responsible for abuse, the charity had expressed concerns about how alerts could inadvertently impact survivors with hidden devices. She noted that having a concealed device to access support without fear of being tracked can offer a lifeline for many survivors.
The government has responded by publishing opt-out guidance specifically for vulnerable individuals. Charities advise victims to deactivate alerts before tests or, if uncertain how to do so, to switch devices off until it is safe to use them again. The alert will activate upon powering a phone back on if it was off during the test.
Cost and Value Assessment
The emergency alert system requires significant investment to maintain. Baroness Neville-Rolfe revealed in Parliament that the total cost of developing the technical architecture and systems, plus the first three years of operational delivery, would reach a maximum of £25.3 million.
Critics have questioned this expenditure, with some branding the alerts intrusive. However, the government maintains the system represents a vital tool to keep the public safe in life-threatening emergencies. The cost must be weighed against the system’s proven ability to reach millions of people within seconds during genuine crises.
Regular testing forms part of this investment, ensuring the system works optimally and familiarising the public with alerts. This approach aligns with standard practice in countries such as Japan and the United States, where emergency alert systems have operated for years.
Public Response and Awareness
The government has invested in public awareness campaigns ahead of tests. These campaigns include accessible materials such as British Sign Language videos and Easy Read content. Communications specifically target drivers and potentially vulnerable groups to ensure everyone understands the system.
McFadden urged the British public to remain composed when hearing the siren-like sound from their phones. He compared the test to fire drills practised in schools and workplaces, emphasising it serves a similar preparedness function. The test message clearly states it is only a drill and requires no action from recipients.
Theatre-goers have been advised to turn off phones before performances, whilst drivers are urged not to be distracted if behind the wheel when alerts sound. Those driving when an alert arrives should find somewhere safe and legal to stop before reading the message.
Looking Ahead
The Emergency Alerts system forms part of the government’s broader Resilience Action Plan, which aims to improve how authorities prepare for and respond to emergencies. The plan includes steps to secure the country and deliver comprehensive emergency preparedness.
Future alerts will continue to focus on situations where there is immediate danger to life. These may include severe flooding, fires, extreme weather conditions, and terrorist attacks. The government will not send alerts frequently, reserving them for genuine emergencies.
The system represents a significant advancement in public safety communications. Its ability to reach millions of people simultaneously, without requiring personal data or app downloads, makes it uniquely suited to modern emergency response. As climate change increases the frequency of extreme weather events, such rapid communication tools will likely become even more critical.
For those seeking additional information, the official government website at gov.uk provides comprehensive guidance on emergency alerts. The site includes details on how the system works, how to opt out if necessary, and advice on preparing for emergencies. Regular updates ensure the public stays informed about system developments and any planned tests.
The Emergency Alerts system has already demonstrated its value in protecting communities during real emergencies. From coordinating evacuations in Plymouth to warning millions about Storm Eowyn’s approach, the technology has proven its worth. As the system continues to evolve and improve based on test results, it will play an increasingly important role in keeping the UK population safe.
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Frequently Asked Questions
Do I need to sign up to receive emergency alerts?
No, the system is completely automatic and requires no registration. All compatible 4G and 5G phones within the alert area will receive messages. The government does not need phone numbers or personal details to send alerts.
Will emergency alerts work if my phone has no signal or data?
Alerts work on 4G and 5G networks without requiring mobile data or Wi-Fi connection. However, phones must be switched on and not in aeroplane mode to receive messages. Older 2G or 3G devices will not receive alerts.
Can I opt out of emergency alerts if I’m concerned about safety?
Yes, users can opt out through their phone settings. iPhone users should go to Settings > Notifications > Emergency Alerts, whilst Android users can search “emergency alerts” in settings. The government advises keeping alerts switched on except in specific circumstances, such as for domestic abuse victims with concealed phones.
How often will the government send emergency alerts?
Alerts are reserved for genuine life-threatening emergencies and will not be sent frequently. Since launching in March 2023, the system has been used five times during real emergencies, including major storms and evacuation operations. Regular tests occur to ensure the system functions correctly.
What should I do if I receive an emergency alert whilst driving?
Do not pick up your phone whilst driving. Continue driving and find somewhere safe and legal to stop before reading the message. The alert will remain on your screen until acknowledged, so there is no rush to read it immediately.
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