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By now, most Tulsans are aware that the city tests its warning sirens at noon on Wednesdays.

So when midday hit Wednesday, the surprise was not that noise was pumping out of the city’s 90 sirens, but that it was a noise most Tulsans had never heard before.

Turns out, Tulsa Area Emergency Management Director Roger Joliff said, a new encoder used to send the test signal — the sound blared for tornado warnings — had accidentally been replaced with the nuclear siren alarm.

“We received a few calls,” Joliff said. “We had some inquiries from people who asked if we had changed tones.”

The new encoder came as part of a project to upgrade 62 of Tulsa’s warning sirens, Joliff said. The encoder — essentially the warning system’s brain — was being tested along with the standard siren test.

Joliff said his personnel knew immediately that the wrong tone was being played, even before the system’s coordinator called to inform him of the problem.