Loud siren-like sounds were triggered on mobile phones and tablets this afternoon as part of a government test of its new emergency alerts system.

The service, coming later this year, will broadcast alarms and send emergency advice to people's devices to warn them of nearby danger that could threaten their life such as a large fire, flooding or a terrorist attack.

As part of the service's gradual roll-out, a number of trials are taking place - including one on Tuesday which fired alarms on some Android phones across the country. A second area-specific planned test is also scheduled for Reading in Berkshire on Tuesday, June 29.

All test-alerts come with a warning message sent to phones included in the trial explaining to users the alarm is only a test-run and nothing to panic about.

The message, which could eventually be replaced with official safety advice when the emergency alert system is running properly, reads: "This is a mobile network operator test of the Emergency Alerts service. You do not need to take any action. To find out more, search for gov.uk/alerts."

But people who don't wish to be disturbed by the alerts, or who would only wish their phone to be triggered in the case of a severe emergency, may be able to turn off some notifications as the system is steadily rolled out to devices nationwide.

The government does not need mobile phone numbers in order to trigger alerts because the warnings are broadcast from phone masts and automatically picked up by devices within range.

You will however, not be able to shut down the most important warnings which come with a risk to life, when the system is operational, says the government website.

The warning says: "You can opt out of some emergency alerts, but not the most important ones. You cannot opt out by subject, only by how serious the emergency is. If you opt out because you do not want flood warnings, for example, you might miss alerts for fires and terrorism.

"Because of this, you should keep emergency alerts switched on for your own safety."

Opting out

Owners of both Android and iPhone devices can see if their phone is already programmed with the new system by searching their phone's settings for 'emergency alerts'.

If your phone has the available settings you'll be able to select and deselect on which levels you'd wish your phone to sound an alarm if ever triggered locally.

Options currently displayed within the settings on some Android devices include Amber, Severe and Extreme - albeit the government insists switching off the most severe level of alert actually won't be possible.

For some Android users, who may have found themselves part of the trials, there may also be an option on their device to switch off test alerts.

This can be found, says the government guide, on included Android phones by also searching for 'emergency alerts' within the phone's settings and turning off 'test alerts' or by opening up the phone calling app and entering the code *#*#2627#*#*. Read more about that process here.

The government is also asking anyone who has a device which sounds during a test event to complete a feedback survey online here.

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