The UK government will be testing its emergency alert system on Sunday, with the vast majority of iPhones in the country expected to receive the notification.
Emergency alert systems around the world occasionally get tested by governments making changes to the infrastructure. As part of the setup of a new system in the United Kingdom, people within the country will experience an alert broadcast on Sunday.
At 3p.m. BST, 10.a.m. Eastern, smartphones and cellular-equipped tablets using 4G and 5G networks in the UK will receive a message from the Emergency Alerts system. The alert itself will consist of a "loud siren-like sound" and a vibration lasting ten seconds, with some devices also reading the alert aloud, according to the government website.
The alert notification will advise recipients that it is a test, that it is a system to warn in the case of a life-threatening emergency nearby, and that device users should follow any issued instructions in a real emergency. It will also advise recipients to visit the UK government's website for more information about the alerts.
In England, Scotland, and Northern Ireland, the message will be in English. In Wales, the message will be in both English and Welsh.
The alerts will work with iPhones running iOS 14.5 or later, as well as Android smartphones running Android 11 or later. Older devices, turned off smartphones, and those in airplane mode will not receive the alert at the time of broadcast.
The alert will sound even if the devices are set to silent, though they can be disabled on an iPhone. Government alerts for many countries can be disabled by going to Settings, selecting Notifications, then under Government Alerts, turning the type of alert on and off.
However, since government alerts are intended to help with emergency situations, threats to safety or life, extreme weather warnings, missing persons broadcasts, and other public safety alerts, it's not advised to turn them off unless absolutely necessary.
Though well intentioned, alert systems do have the potential to cause panic. In 2018, a false emergency alert was broadcast in Hawaii warning of incoming ballistic missiles, which prompted the FCC to make changes to the U.S. system.