Classroom Noise Meter

How it works — and why audio never leaves

When you click Start microphone, the browser asks for permission. If you grant it, the page receives a live audio stream and pipes it into a Web Audio AnalyserNode — the same primitive that powers visualizers in music apps. The analyser produces a small array of recent waveform samples; the page squares each sample, averages them, takes a square root, and ends up with one number: the room's current root-mean-square volume. That number drives the bar.

The smoothing you see on screen is a light low-pass filter on that number, so the bar settles in tenths of a second instead of jittering on every single sample. The animation runs through requestAnimationFrame, so it scales with your display's refresh rate and idles when the tab is hidden.

The audio stream is never written to a buffer beyond the current analysis window, never combined into a recording, and never sent to a server. There is no MediaRecorder involved, no fetch, no WebSocket — the page simply has no networking code that runs at all. Clicking Stop calls track.stop() on every audio track and suspends the audio context, which is what makes your browser's "recording" indicator turn off.

Microphone permission is also only requested when you explicitly click Start — never on page load. The "no recording" claim is enforced by what is and isn't in the source, not by a promise: the page is small and unminified, so a developer or curious district IT staffer can read the whole file.

Using it on a projector or smartboard

1. Open the page in your classroom browser on the projector display. Click Start microphone and grant permission once. (Most browsers remember the choice for that site.)
2. Click Full screen. The meter expands to fill the display and the zone label becomes readable from the back row.
3. Adjust the two threshold sliders for the activity. The working threshold sets where Calm becomes Working; the loud threshold sets where Working becomes Too loud.
4. If the bar is hugging one end, slide the Sensitivity control — lower for a noisy room, higher for a quiet one — or click Calibrate to room to sample a couple of seconds of ambient level and pick a sensible baseline.
5. To turn it off, click Stop. The microphone releases and the browser's recording indicator goes away.

Most teachers leave the meter running through one activity, then tweak the thresholds for the next one. Your settings stay between sessions — labels, thresholds, sensitivity, and the alert toggle are all kept in your browser's local storage, so the next time you open the page everything is where you left it. (Closing the tab or clearing site data wipes them.)

Setting the zones for your room

There is no universally correct level for "too loud" — a kindergarten room mid-project sounds different from a high-school seminar, and even the same room sounds different at 8am and 2pm. The thresholds are sliders rather than fixed decibel numbers on purpose: you set them to where this room, this activity, this group of students actually crosses the line.

• Silent reading. Working threshold low (e.g. 20), Too loud threshold moderate (e.g. 45). Even quiet whispers will trip Working, which is the point — the bar reinforces that silent reading is silent.
• Independent practice. Working threshold moderate (e.g. 35), Too loud threshold around 65. A bit of pencil tapping and chair shifting stays in Calm; quiet conversation moves into Working; off-task volume hits Too loud.
• Partner discussion or group work. Working threshold higher (e.g. 50), Too loud around 80. Discussion lives in Working by design; only genuine "too loud to think" volume tips Too loud.
• Lab or shop activity. Working high, Too loud as a real safety/communication ceiling so you can hear instructions when needed.

Two threshold sliders are enough to encode most of those activities. Three zones is also a deliberate ceiling — students can act on green/amber/red signals at a glance; more colors invite ambiguity. The labels are editable, so if your room talks about "Library voices / Group voices / Outside voices," the meter can show those words instead.

Classroom-management notes

A noise meter is a tool, not a behavior plan, and it works best when it replaces a teacher behavior that the meter does better. Three small changes usually follow:

• Less voice strain. The bar turning amber is a visual cue that doesn't require you to raise your voice or interrupt. Students start to self-correct against the color before you say a word.
• More agency. The threshold for "Working" is visible. The class knows what counts as acceptable for this activity instead of guessing at the teacher's mood. That visibility tends to drop the average volume on its own.
• Cleaner transitions. When the meter is up, "let's get back to Calm" lands as an instruction students can verify, not a vague request.

A few warnings worth knowing. The meter is not a competition. Hanging consequences on whether the bar crosses a line tends to make students perform quietness loudly, which is its own problem. The meter is also not perfectly fair — a kid right next to the laptop affects it more than a kid in the back, which can read as singling out the wrong person. Better used as ambient feedback for the whole room than as evidence in a specific call-out.

Some classrooms pair the meter with a visible countdown timer during timed activities — both projected, both readable from the back. The combination of "how long do I have" and "how much noise is okay" is most of what students need to self-regulate in a work block.

Free, no signup, your audio stays on your device

This page is a deliberately small alternative to all-in-one classroom dashboards that include a noise meter behind a signup. There is nothing wrong with those products; they just are not what this is. This is one tool, free, no account, no campus license required. The page does not phone home, and the audio path lives entirely in the browser.

If a district IT person needs to verify that nothing leaves the network: the page makes no XHR or fetch calls during operation (you can see this in the developer tools' Network tab), and the audio is never written to a recordable buffer. The source is small enough to read in an afternoon.

Need other free classroom utilities with the same privacy stance? Browse the teacher tools collection — name picker, timer, group generator, attendance sheet, grader, and more. Or open the full tools index for the whole list.

Frequently asked questions