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The test of the Government’s mobile alert message system will take place between 6pm and 7pm.
All mobile phones that are switched on, in coverage, and that are capable of receiving it will be automatically sent the alert.
This emits a loud warning sound and shows a warning message. The alerts are sent automatically, using cell broadcast technology, and there is no way to opt out of the service.
Emergency Management Otago director Chris Hawker said the messaging system was a "21st century" measure, and a potentially life-saving improvement to alert people in emergencies.
"It’s a serious thing, done for a serious reason and should be seen in a very positive light," Mr Hawker said.
He was "pretty optimistic" that cellphone users would not be confused by the test warning message.
If the technology had been available, the alerts would have been sent out during the July floods on the Taieri Plain and after the Kaikoura earthquake late last year, he said.
After that earthquake many people, including those in emergency management, realised that tsunami alerts had to be improved.
He advised people receiving the mobile phone alert to "read the message".
"Understand what it’s about, appreciate what it’s there for."
If people ever heard the alert again, and it was not a published test, "then follow the instructions", he said.
Perhaps only about one-third of cellphones would be capable of receiving the emergency message initially, but as people bought new phones and updated older models, it was hoped about 80% of cellphone users could eventually receive the alerts, he said.