The British government says it will launch a review after many smartphone users complained they did not receive a nationwide emergency alert test.
Millions of people across the UK heard an alarm on their phones on Sunday afternoon, local time, while many others did not.
The government was testing an alert that could be used to warn about dangerous situations including fires, flooding or terrorist attacks.
The alarm lasted for around 10 seconds on 4G and 5G devices. It sounded a siren-like noise, while the words "Severe Alert" appeared on the screen.
The test was scheduled for 3pm local time.
But people claimed to have received it early, late, and in some cases, not at all.
Social media users were quick to see the funny side.
One wrote: "As so many of my ex-girlfriends said in the past, ‘Was that it?’"
Another tweeted: "Have heard U2 has snuck an entire album into todays emergency alert test."
Love Island contestant Jessie Wynter posted a TikTok of her boyfriend Will Young who was confused by the alert.
Comedian Richard Osman chimed in: "Didn't realise the Government emergency alert at 3pm was going to be about the Spurs score," he tweeted.
Spurs were beaten 6-1 in the Premier League on Sunday afternoon.
Questions over why alert didn't go off for some
Although it gave the users who received the alert a fright, many people didn't receive the emergency test at all.
"15:04 and still no emergency alert," one person tweeted.
Another said: "My emergency alert didn't come so I guess I'm the first one to die during a nuclear war."
A spokesperson for the UK'S Cabinet Office told BBC it was aware some people hadn't received the alert and would "be looking at this as part of our review of the test".
Deputy Prime Minister Oliver Dowden said the sound could save people's lives.
Those who received the alert received a text which 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 you and others safe."
The government also advised mobile phone users to make sure their phones had the latest software updates to get any future alerts.
