Health experts warn UK emergency alert test may trigger cardiac events in vulnerable people

The UK government's national emergency alert system, due to be tested for the second time on Sunday at 3 p.m., could provoke dangerous stress responses in a small number of people with underlying heart conditions, a health expert warned.

The test will send a siren-like noise and an on-screen message to 4G- and 5G-enabled phones and tablets across the country as part of exercises designed to ensure the system can deliver "life-saving information" during wildfires, storms and other major incidents.

Dr. Luana Main, an expert on acute stress responses at Deakin University, told the Daily Mail that sudden alarms can activate the body's fight-or-flight reaction and, in rare cases, could trigger a cardiac event in people with pre-existing cardiac vulnerabilities. "Sudden alarms like those used in emergency services can activate our flight-or-fight response, which is our body’s way of dealing with a sudden threat or stressor, even when there’s no actual danger," she said. "In some rare cases, for individuals with underlying cardiac vulnerabilities, it is possible that it may trigger a cardiac event."

Government officials have described the alerts as a means to transmit urgent instructions to the public during fast-moving incidents. The first nationwide test of the system took place earlier this year. This Sunday's exercise is billed as the second national test and will reach millions of devices simultaneously.

People who are concerned about the potential health effects of the test can disable emergency alerts on many devices, but methods vary by make, model and operating system. On Apple iPhones, emergency alerts are typically controlled through Settings > Notifications, where a "Government Alerts" or "Emergency Alerts" toggle can be disabled. On Android devices, alerts are usually found under Settings in sections labelled "Safety & emergency," "Wireless emergency alerts" or "Emergency alerts," where individual alert types can be switched off. Users should consult their device manual or the manufacturer's online support pages for precise instructions.

Medical professionals and emergency planners caution that opting out may prevent recipients from receiving genuine life-saving warnings. Clinicians advised that anyone considering disabling emergency alerts should weigh the risk of missing critical instructions against personal health concerns and, if necessary, seek personalised advice from their cardiologist or general practitioner.

The alert system was introduced to provide a rapid channel for public safety messages when other communications channels are likely to be overwhelmed or to deliver urgent, location-specific instructions. Officials have emphasised that tests allow authorities to check technical performance, refine messaging and ensure the system reaches as many people as possible.

Experts on stress and cardiovascular health say that abrupt, loud alarms can briefly increase heart rate and blood pressure as part of the acute stress response. For most people this is transient and not harmful, but people with unstable cardiac disease, recent heart attacks or certain arrhythmias may be more susceptible to adverse effects. Healthcare providers advise patients with serious heart conditions to discuss individual risks and coping strategies, including stress-management techniques and whether additional precautions are warranted during public alert tests.

The government has not indicated that the national test will include any content beyond the standard siren and message advising it is a test. Recipients are asked to follow any specific guidance issued by official channels and to report concerns to their healthcare provider or local emergency services if they experience symptoms during or after receiving the alert.