How the UK's emergency alerts on mobile phones work
What the government's Emergency Alerts system is, why it sounds even on silent, what it does and does not know about you, and how to switch alerts off.
The UK's Emergency Alerts system lets the government and emergency services send a warning directly to mobile phones in an area where there is a danger to life. The message arrives with a loud siren-like sound and vibration that is designed to be impossible to miss, even if the phone is on silent.
When alerts are used
Alerts are reserved for serious, immediate risks. The government's guidance gives examples such as severe flooding, fires, explosions and terrorist incidents. They are not used for routine weather warnings, traffic news or general announcements.
Authorities that can request an alert include the government, the emergency services and agencies such as the Environment Agency. Each message tells you what is happening in your area and what to do, for example to leave a particular area or stay indoors. Many include a link to GOV.UK or another official site for more detail.
How the technology works
The system uses cell broadcast, a technology built into mobile networks. Instead of sending a text to a list of phone numbers, the network broadcasts a message from specific mobile masts. Every compatible phone connected to those masts at that moment receives it.
This has several consequences.
- The government does not need your number. No phone numbers are collected or stored to send an alert.
- It does not track you. Cell broadcast is one-way. Your phone receives the message but does not report back that it is there or who you are.
- Location is approximate. An alert reaches the masts covering the affected area, so people just outside the boundary may receive it, and people inside it may occasionally miss it.
- Busy networks are not a problem. Because it is a broadcast rather than individual messages, it is not delayed when lots of people are using their phones.
Alerts go to compatible smartphones on 4G and 5G networks. Phones that are switched off, in flight mode, or connected only to older networks will not receive them, and nor will Wi-Fi-only tablets. Most phones running recent versions of Android and iOS are compatible.
What to do when one arrives
Read the message and follow its instructions. The alarm lasts around ten seconds. You can stop the sound by acknowledging the alert on the screen.
If you are driving, do not read or respond to the alert. The Highway Code rules on using a handheld phone still apply. Find somewhere safe and legal to stop first, or ask a passenger to read it.
If you are a carer for someone who would be distressed by a loud alarm, or you rely on a phone for something else that could be disrupted, it can help to explain in advance what the sound means.
People who are deaf or hard of hearing can still be alerted by the vibration and the on-screen message.
Switching alerts off
You can opt out, although the government recommends keeping alerts switched on because they may contain life-saving information.
On most iPhones, go to Settings, then Notifications, and scroll to the bottom to find the toggles for severe and extreme alerts. On Android phones the setting is usually under Safety and emergency or Notifications, labelled Wireless emergency alerts, though the exact location depends on the manufacturer. If you cannot find it, search the settings app for "emergency alerts".
Some people at risk of domestic abuse keep a second phone hidden. Because an alert would make it ring loudly, the government's guidance suggests switching alerts off on any such device.
Scam messages sometimes claim to be emergency alerts. A genuine alert never asks you to reply, give personal details or make a payment. If a message does, it is not from the government.
