The stop light turned red Friday after recess, setting off the Yacker Tracker siren in a first-grade classroom.

The 6- and 7-year-old students at Marigold School knew that meant they were being too loud. But they didn't know a Chico woman invented the machine.

Teacher Brian Holderman said he first saw the Yacker Tracker in a colleague's classroom and learned that a friend, Fran Rebello, conceptualized, designed and sold the device. So he called her, got one and started using it in his classroom about five years ago.

"I think first-graders forget how to whisper," Holderman said....