Britons urged to ‘keep their cool’ as siren-like sound to emit from millions of devices on Sept 7 at 3pm

At about 3pm this coming Sunday all 4G and 5G mobile phones in the UK will blare a 10-second siren blast and display a test alert.

Millions of UK phones to sound siren in national emergency alert test, part of government resilience efforts.

Millions of phones will emit a siren sound and vibrate during the drill

It marks the second test of the national emergency alert system after the first in 2023