The national system for sending emergency alerts to mobile phones will be tested for the second time on Sunday 7 September.

The alerts are designed for situations where there is an imminent danger to life, such as during extreme weather events or a terror attack.

The previous test, in April 2023, revealed a number of technical issues – with some people getting the alert more than once and others not receiving it at all.

The text of the message will read:

“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 alert will be sent to all smartphones on the UK’s 4G and 5G networks, even if they are not connected to mobile data or wi-fi.

There are about 87 million mobile phones in the UK and the goverment says about 95% of the population has 4G or 5G access.

Older phones, and phones connected to 2G or 3G networks, will not receive the message.

Phones that are switched off or in airplane mode will also not get the alert.

During the 2023 test, many mobiles phones on the Three network did not get anything, along with some users on other networks. Others received multiple messages.

The government later confirmed that the alert had not reached around 7% of compatible devices, and promised to address technical issues before future tests.

The government strongly recommends that users enable devices to receive alerts, but it is possible to opt out.

This can be done by searching in your phone’s settings for “emergency alerts” and turning off “severe alerts” and “extreme alerts”.

The government has published a guide on how to opt out of the test.

Ahead of the first test, domestic abuse charities warned that the alert system could potentially endanger victims by alerting an abuser to a secret phone.

The National Centre for Domestic Violence advised people with concealed devices to make sure they were turned off for the duration of the test.