On Sunday, millions of phones blared an emergency signal simultaneously under a UK-wide government test. However, a number of handsets received the alert late – or not at all.
Here we answer your questions on what happened.
Did the alert go as planned?
Phones around the UK sounded and vibrated an alarm at 3pm on Sunday for 10 seconds, accompanied by a text message headlined “severe alert”. It stated: “This is a test of emergency alerts, a new UK government service that will warn you if there’s a life-threatening emergency nearby.”
The government said it had “effectively completed” the test, describing it as “the biggest public communications exercise of its kind ever done”. It was intended to reach a substantial proportion of the estimated 85m mobile phones in the country, with only those too old to connect to a 4G network or without a software update in the last two years expected to miss out.
However, not all users received it at the right time, or in some cases at all. The government said a small number of phones did not receive the alert. It said it was “working with mobile network operators to review the outcome and any lessons learned”.
The Three network appeared to be the most affected. It said: “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 users on the O2 and Vodafone networks also reported difficulties, while some reported receiving the alert a minute early – or 20 minutes later.
Why did some Three users not receive the alert?
Unlike in the pandemic, when SMS alerts were sent specifically to individual numbers, Sunday’s alert was broadcast via the mobile phone masts that form the core of the nation’s 4G and 5G networks. It means that if you were within range of a mast, you should have received an alert.
However, what appears to have happened on the Three network is a configuration error preventing the majority of users receiving the alert. The “cell broadcast system” that underpins the alert is a fundamental part of the international standard for mobile phones, and the technology of mobile masts requires networks to send out the alert at regular intervals to ensure it is picked up by all phones. Most networks did just that, repeating the pulse multiple times a second for up to 20 minutes, to ensure that users with intermittent coverage still received it.
But according to signal analysis, Three apparently sent the signal out just once, at 3pm on the dot, ensuring that only those phones that were actively connected to the network at exactly that millisecond received it.
What can the government and mobile phone networks learn from the alert?
Top of the list will be uncovering the chain of events that led to many customers on Three’s network not receiving the alert, and trying to uncover similar root causes for other failures to deliver the alert. A small amount of users on other networks also reported the message failed to be delivered on their devices.
As well as the technical feedback, the government will want to assess reactions to the alerts. Earlier trials had found a number of difficulties to be overcome, including the problem that the alert itself is disruptive enough that users raced to dismiss it in order to silence the alarm – without actually reading the warning itself.
Was it disruptive?
The alert had been so well trailed that disruption was minimal. Play was halted at the World Snooker Championship in Sheffield to allow for the alert, while the alarm sounded during a live BBC news segment on the alert and some runners at the London marathon had their warmdown interrupted.
However, the test was for a system whose purpose is for local or national emergencies, so when it is used in earnest it is likely to cause more disruption. Because the system uses the mobile phone broadcast network, alerts can be limited to specific areas affected by, for instance, flooding, while the rest of the country goes about its business undisturbed.
Some users may choose to turn off alerts on their phones as a result. “Extreme” and “severe” alerts can be disabled on all phones, but the system also allows for an even higher tier of severity, named “presidential” in the international standards but renamed “government” in the UK. That tier cannot be disabled except on a few Android phones, but it is (hopefully) unlikely to ever be used.
