The system is designed to help protect lives by delivering urgent safety advice directly to mobile phones during major emergencies.
Mobile phones connected to 4G and 5G networks will receive the alert at around 3pm on Sunday 7 September.
The drill follows the use of the system in Wales during Storm Darragh in December 2024, when a rare red weather warning was issued. The alert was authorised by UK Government minister Pat McFadden.
Around three million people across Wales and south‑west England received the message, which warned of dangerous and potentially life‑threatening conditions.
During the national test on 7 September, mobile phones will vibrate and emit a loud siren‑like sound for up to ten seconds. A test message will appear on screens, making it clear the alert is a drill.
Jo Stevens, Secretary of State for Wales, said:
On Sunday 7 September at around 3pm, mobile phones on 4G and 5G networks across Wales and the whole of the UK will vibrate and emit a loud siren-like sound for up to ten seconds, marking one of the biggest public safety exercises in our nation’s history.
There’s no app or sign-up, just a life‑saving alert when it matters. This UK‑wide test will help ensure it works as it should when we need it.
We used the system during Storm Darragh to alert around three million phones when there was a red weather warning meaning lives were at risk.
Ahead of the test, the government is running a public information campaign to notify people it is taking place, including communications targeted at vulnerable groups such as victims of domestic abuse. The campaign has featured the first national information video in British Sign Language.
Last week, the full text of the test message was revealed for the first time, saying:
This is a test of Emergency Alerts, a UK government service that will warn you if there’s a life-threatening emergency nearby.
You do not need to take any action. In a real emergency, follow the instructions in the alert to keep yourself and others safe.
Find simple and effective advice on how to prepare for emergencies at gov.uk/prepare.
Visit gov.uk/alerts for more information or to view this message in Welsh. Ewch i gov.uk/alerts am ragor o wybodaeth neu i weld y neges hon yn y Gymraeg.
The test will be just the second of its kind and follows a government commitment to test the system regularly to make sure it works optimally and familiarise the public with the alerts. This is in line with standard practice in other countries, such as Japan and the USA.
As well as making clear the test is just a drill, the message will point the public to GOV.UK/PREPARE, a one‑stop website offering practical advice about steps households can take to prepare for emergencies.
