The UK will conduct its first test of a new emergency alert service on Sunday, with millions of mobile phones set to emit a loud alarm and vibrate at 3:00 pm (1400 GMT).
The national system, modelled on similar schemes in Canada, Japan, the Netherlands and the United States, aims to warn the public if there is a danger to life nearby but has generated criticism over "nanny state" intrusion.
A message 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."
System to alert people during disasters
Emergency services and the government hope to use the system to alert people to issues such as severe flooding and fires.
The 10-second alarm, which will sound even if phones are on silent, is expected to disrupt entertainment and sporting events, including Premier League football matches.
Organisers of the World Snooker Championship will pause play just before the alert, while the Society of London Theatre has advised its members to tell audiences to turn off their phones.
Drivers have been warned not to pick up their phones during the test, and people who do not wish to receive the alerts can opt out in their device settings.
"Keep Calm and Carry On. That is the British way and it is exactly what the country will do when they receive this test alert at 3:00 pm today," said Deputy Prime Minister Oliver Dowden.
"The government's number-one job is to keep people safe and this is another tool in the toolkit for emergency situations."
