Nice and calm
The screen stays green while it's calm, goes amber as it gets louder, and flashes red with one beep when it stays too loud for a few seconds.
Tap Start, then allow the microphone when asked.
Nice and calm
The white bar is the noise right now. Slide the dot to where you'd tell the children to quieten down: once the bar stays past the dot for a few seconds, the screen goes red and beeps.