Overview

• Supported 4G and 5G phones and tablets will vibrate and emit a loud siren for about 10 seconds even if set to silent.
• Devices that are switched off or in airplane mode will not receive the test alert.
• The government estimates the broadcast could reach about 95% of roughly 87 million devices, though the 2023 test left some compatible phones without alerts.
• Authorities have issued opt-out instructions and cautioned domestic abuse survivors that a hidden device could be exposed by the alert, with guidance at gov.uk/alerts/opting-out.
• A public information campaign with British Sign Language materials is underway, and officials note five real alerts have been issued since the system launched in 2023.