Millions of people across the UK were waiting by their phones on Sunday, April 23, in anticipation of the alert test by the UK Government.
Designed to save lives, the alert will be used in life-threatening situations including flooding and wildfires.
Lasting around 10 seconds, many phones starting going off at 2.59pm with some just on time and others a while after.
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And while many ended up getting the notification, others did not.
Taking to Twitter one said: "Didn't get an emergency alert! Should I be worried? Is THAT an emergency?!"
Another added: "Shoutout to all my UK homies who didn't get the test emergency alert . We are NOT making it when the apocalypse breaks out."
"Out of 6 people at the table one person got it early and the rest didn't get it #emergencyalert" tweeted a third.
Here's why that may have been.
Three network users
In a tweet, Three said that they were aware some of their customer did not get the alert with many on the network tweeting they received it as much as 15 minutes late and some, not at all.
They wrote: "We're aware that a number of customers have not received the test alert. We're working closely with the government to understand why and ensure it doesn't happen when the system is in use."
Some Three customers did however receive the alert.
Other reasons your phone may not have received the alert
The alert relies on towers that use 4G or 5G, so if you were only connected at 3G at the time the test alert was sent, then your phone would not have been capable of receiving it.
As well as this, your phone may also have the emergency alert settings switched off.
Despite being an automatic alert, it is possible to switch them on iPhones and Androids by going into settings, typing 'emergency alerts' into the navigation bar and switching the 'Extreme Alerts' button to on.
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