Review to investigate why some phones did not receive emergency alert

According to the Cabinet Office, while the “vast majority” of compatible phones received the alert, “a very small proportion” of mobile users on some networks did not receive it.

The alert was broadcast at 3p.m. on Sunday and should have been received by every 4G and 5G device across the UK.

Customers on the Three network appeared to be most affected by reports that some users did not see or hear the alert, which the firm acknowledged on Twitter.

“We’re working closely with the government to understand why and ensure it doesn’t happen when the system is in use,” it said.

Further still, a small number of people said that since the alert went off on their device, their phone had not been able to make or receive calls.

In Wales, the test was broadcast in the Welsh language but contained an error. For the words “others safe”, the message read “eraill yn Vogel” when it should have been “eraill yn ddiogel”.

The UK government blamed a “technical error” for the mistake and said this would be rectified in future.

The Cabinet office said it was looking into these issues alongside reports that some people did not receive the alert until some time after they were meant to.

An awareness campaign of the test was launched to ensure the public knew it was going to occur. According to Cabinet Office polling, 88 per cent of the British public were made aware.

The system will be an additional tool designed to issue warnings when there is an imminent risk to life such as flooding or terror attacks.

Announcements and signage across the transport network were put in place in the run-up to the test.

The National Centre for Domestic Violence had previously warned people with hidden second mobile phones to turn off the alerts to avoid revealing the location of their devices.

“Hidden second mobiles are an emergency lifeline for victims and survivors living under the constant threat of abuse, or worse,” the body said.

“This siren test may unexpectedly reveal their presence to abusers – with disastrous consequences.”

Officials have stressed that it is easy to opt out of the system if people need their phone to stay concealed, either by turning off the alerts or simply having the phone switched off during the test.

Early testing on the system began in 2014, with the first test alert sent in March 2020. The Emergency Alert System was formally launched on 19 March prior to yesterday’s nationwide test.