UK emergency-alert system: What is it and when is the test?

A UK-wide emergency alert system will be tested on Sunday.

A message is set to appear on the home screens of mobile phones and tablets from 15:00 BST, accompanied by a loud siren-like sound or vibration lasting for about 10 seconds.

The government says the new system is a "vital tool to keep the public safe in life-threatening emergencies".

The test alert will say: "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."

Phone users can swipe away the alert message or click "OK" to continue using their phone as normal.

The alerts will work on all 4G and 5G phone networks and on devices with the following software:

Older "non-smart" phones will be unable to receive the alerts, and nor will devices that are turned off or on aeroplane mode.

The alert will sound on phones on silent mode.

The government says emergency services will have other ways to notify those without a compatible device.

The alert is expected to reach about 90% of mobile phones.

Despite the government strongly recommending enabling devices to receive alerts, users can opt out.

This can be done by searching in settings for "emergency alerts" and turning off "severe alerts" and "extreme alerts".

Personal data about a user's device or specific location will not be collected or shared, according to the Cabinet Office.

The alerts will be broadcast from mobile-phone masts to every compatible phone and tablet within range.

The government or emergency services do not need to know the mobile-phone number or any other personal data.

Domestic-abuse campaigners, including the charity Refuge, warn the test could endanger some vulnerable people by potentially alerting an abuser to the location of a hidden phone.

The government says it has been engaging with the organisations to ensure vulnerable people were not adversely affected. Refuge has produced a video showing how to turn off the alerts.

Drivers are also advised not to look at or touch their phone until it is safe to do so, just as when receiving calls or messages.

Emergency alerts, with advice about how to stay safe, will be sent - locally or nationally, by the government or emergency services - on rare occasions where there is a threat to life.

They will initially focus on the most serious weather-related events, such as:

But many people will not receive an alert for months, perhaps even years.

Many countries around the world use emergency-alert systems, including the United States, the Netherlands and Japan.

Japan credits its system with saving countless lives in natural disasters.

The US system allows the president to send a message to citizens directly.

But it does not always go to plan.

In 2018, in the US state of Hawaii, an alert warning of an incoming missile was sent in error, causing widespread panic.