Overview

• Compatible 4G and 5G phones and tablets will vibrate, emit a loud siren for about 10 seconds and display a test message that overrides silent mode.
• Mobile networks including O2, EE, Vodafone and Three are texting customers in advance to explain the drill and direct them to gov.uk/alerts.
• Domestic abuse charities advise people with hidden devices to switch off Severe and Emergency Alerts in settings, and the Epilepsy Society warns the siren could trigger seizures for some.
• Police penalties for handheld phone use still apply during the test, with guidance to pull over safely before acknowledging the message.
• The system has issued five real warnings since 2023, the last nationwide test missed about 7% of compatible devices and this exercise aims to validate improvements, with older or 2G/3G-only or Wi‑Fi‑only devices unlikely to receive it.