THOUSANDS of Brits did not receive today's emergency alert test - and the reason has now been revealed.
Many Brits were left in the dark when phones started ringing with the alert at 3pm and now it's been revealed it's because the network they use was experiencing technical difficulties.
The Three mobile network has admitted that some of its users did not receive the alert.
In a statement, a Three spokesperson said: "We are aware that a number of customers have not received the test alert.
"We are working closely with the government to understand why and ensure it doesn’t happen when the system is in use."
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The Cabinet Office said that, while the vast majority of compatible phones received the alert, officials were aware that a "very small proportion of mobile users on some networks did not receive it".
The department explained the failures would be looked into as part of the review of Sunday's test.
A government spokesman said: "We have effectively completed the test of the UK-wide Emergency Alerts system, the biggest public communications exercise of its kind ever done.
"We are working with mobile network operators to review the outcome and any lessons learned."
Three's admission came after users flooded Twitter with complaints they failed to receive the national siren.
Ann Martin tweeted: “I am with Three and did not get it - am confused as to the reasons why.”
And fellow Three phone user Kate Bevan joked: “I guess those of us on Three have been deemed expendable, then.”
Another Twitter user wrote: "Well, that was an anti-climax, did not work on the Three network in South Derbyshire."
While another added: "Didn’t work for anyone in my family and we’re all on ThreeNetwork and One on IDmobile."
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Three - along with O2, Vodafone and EE - runs its own network and does not piggyback on others' like Tesco Mobile.
Technology expert Will Guyatt said: “We don’t know whether the government will be embarrassed or just frustrated.
“But Three is not the network you’d want in a nuclear apocalypse.”
About 85 million phones on 4G and 5G were due to hear a ten second alarm at 3pm.
The emergency test was the same volume as a ringtone as it vibrated handhelds and came with a 'Severe Alert' message.
It read: "This is a test of Emergency Alerts, a new UK government service that will warn you if there's a life-threatening emergency nearby.
"In a real emergency, follow the instructions in the alert to keep yourself and others safe.
"Visit gov.uk/alerts for more information. This is a test. You do not need to take any action."
But the jolting alarm shocked some Brits and even set off dogs who were heard barking up and down the country.
Those who did get the alarm took to Twitter seconds to post how terrifying it was seconds later.
One person said: "The emergency alert system just scared the f*** out of me."
A second added "that alert was a bit loud" while another joked "it was so dalek like".
Others reported receiving the alert at different times, while some said theirs was narrated.
One person wrote on Twitter: "Confusingly my wife’s alert went off a min before mine - same phone, same network, in the same room."
The Government say the system will make it easier for the public to be notified of major incidents like terror attacks and severe weather.
