How to use Noisecatcher
A step-by-step guide to measuring, mapping, and acting on noise pollution.
Install as an app
Installing adds Noisecatcher to your home screen and lets it run full-screen and offline. It is optional — everything works in the browser too.
Getting started
Noisecatcher uses your device's built-in microphone to measure ambient sound levels in real time. It works entirely in your browser — no account, no installation, and nothing leaves your device unless you choose to export.
Open the Meter page
Allow microphone access
Hold your phone steady
Wait for stabilisation
Stop measuring or generate a report
Reading the gauge
The large arc gauge displays the current sound level in decibels (dB). The value shown is a short-term average (Leq), not a peak. Decibels follow a logarithmic scale — a 10 dB increase means roughly double the perceived loudness.
Normal conversation, quiet office, birdsong.
Busy restaurant, TV at normal volume. WHO recommends limiting exposure.
Heavy traffic, loud music, lawnmower. Long exposure causes hearing damage.
Motorcycles, concerts, power tools. OSHA limit: 90 dB over 8 hours.
What each readout means
Noise reports
A noise report captures the complete picture of a measurement session in a single shareable document — statistics, health context, psychoacoustic profile, dose, and optionally a voice commentary. Reports are stored permanently in your device and can be printed or saved as PDF.
Start measuring
Tap 'Stop & Report'
Review the report
Add a voice note
Print or save as PDF
Each report records
Leq (energy-average), Peak, L10, L50, L90 (percentile levels)
EU Directive 2003/10/EC noise dose (80 dB / 8 h reference)
OSHA PEL noise dose (90 dB / 8 h reference)
Loudness (sone), Sharpness (acum), Roughness (asper), Psychoacoustic Annoyance
Acoustic Complexity Index (ACI)
HF deterrent scan — 15–20 kHz band energy
Calibration offset applied
Optional voice note attachment
/report/[id]) and it will load the same data on the same device. The data lives only in your browser's IndexedDB.Dropping pins
A pin saves your current dB reading, GPS location, timestamp, and bearing (compass direction) as a single data point. Pins are stored locally on your device — they are never uploaded.
Start measuring
Wait for a stable reading
Tap 'Pin this reading'
View your pin on the map
Each pin records
dB level (current reading at time of pin)
GPS coordinates (lat/lng)
Timestamp (ISO 8601)
Compass bearing (if orientation permission granted)
Noise category (safe / caution / dangerous / critical)
Noise source categories
When dropping a pin, you can tag the type of noise source. This makes your data far more useful for advocacy, legal complaints, and research — a lawyer or city official can immediately see whether you documented construction drilling, an ambulance siren, or gunfire.
How the picker works
Step 1 — choose a category. A row of category buttons appears in the pin form. Each one represents a top-level noise type (Traffic, Emergency, Construction, etc.). Tap one to select it.
Step 2 — choose a subcategory. As soon as you tap a category, its specific subtypes appear directly below — no new screen, no menu diving. Tap the exact source that matches.
Skip if unsure. Tapping Any / skip saves the pin without a source tag. The dB reading and location are still recorded.
sourceSub field. When you share your data with city authorities, legal aid organisations, or researchers, this field allows them to filter and analyse specific noise types — far more useful than a raw dB number alone.Using the map
The Map page shows all your saved pins on an interactive OpenStreetMap map. Each pin is colour-coded by severity and shows a directional arrow for bearing.
Green pin — Safe (0–54 dB)
Below WHO recommended thresholds. Documenting quiet areas is as valuable as documenting loud ones — they establish a baseline.
Yellow pin — Caution (55–69 dB)
Within range WHO recommends limiting for long-term outdoor residential exposure.
Orange pin — Dangerous (70–84 dB)
Exceeds WHO 70 dB threshold for leisure venues. Chronic exposure at these levels degrades hearing.
Red pin — Critical (85+ dB)
OSHA occupational safety limit. Short-term exposure (< 30 min) at 100 dB can cause permanent hearing damage.
Map controls
Voice notes
Voice notes let you record up to 60 seconds of audio commentary and attach it to a noise report or a notebook. Use them to describe the context, the noise source, or your reaction — information that numbers alone cannot capture.
Find the voice recorder
Start recording
Stop recording
Play or delete
Field Notebooks
A field notebook is a named container that groups pins, reports, and voice notes belonging to the same noise problem — a building site near your home, a neighbour's sound system, a road you cross every day. Building a notebook over time creates a structured, chronological dossier you can share with authorities or legal counsel.
Create a notebook
Open the notebook
Link future recordings
Use as a dossier
Exporting your data
All pins are stored only on your device (IndexedDB). To preserve your data, share it, or use it in external tools, export it as GeoJSON.
Go to the Map page
Tap '↓ Export GeoJSON'
.geojson file will be downloaded to your device.Use your data
db, timestamp, category, bearing.Field recording practice
Your smartphone is an acoustic instrument. These practices improve measurement consistency, protect recordings from artefacts, and align your method with the counter-forensic ethos of Noisecatcher.
Position the microphone correctly
Hold the device at chest height, microphone facing the sound source. Most smartphones have their microphone at the bottom edge. On iPhones, the primary mic is at the bottom; a second mic for noise cancellation is at the top or rear — this one is not used by the Web Audio API. Avoid covering the mic grille with your palm or case material.
Stabilise before you read
The Leq (energy average) takes 2–3 seconds to stabilise. Wait for the ● LEVEL indicator to turn green before dropping a pin. Transient sounds in the first second (traffic passing, a door closing) will skew the reading if you measure too quickly.
Keep the device still
Movement creates handling noise. Rest the device on a surface, use a small tripod, or brace it against your body. If you are measuring a stationary source (HVAC unit, transformer, construction site), a fixed position gives more reproducible results. Note your exact position in the pin description for future reference.
Manage wind noise
Wind across the microphone generates low-frequency turbulence that inflates readings by 5–15 dB. Outdoors: shield the mic with a foam windscreen (any lavalier foam works), a piece of fabric, or by pointing the device slightly away from the wind. Note wind conditions in your pin description. Readings taken in wind above Beaufort 3 should be flagged as unreliable.
Enable Airplane mode
Incoming calls, SMS, and cellular radio events cause electromagnetic interference that appears as brief spikes or a rhythmic buzzing at ~217 Hz (GSM) in recordings. Switch to Airplane mode — then re-enable Wi-Fi only if you need maps or federation data. This eliminates RF artefacts from your measurements.
Avoid Active Noise Cancellation
Never use earphones with Active Noise Cancellation (ANC) when measuring. ANC earphones include a pass-through microphone whose input has been electronically modified. The signal Noisecatcher receives will not reflect the actual acoustic environment. See the About page for the full ethos argument.
Use an external microphone when possible
An omnidirectional lavalier (worn at chest height) gives a more consistent, body-referenced measurement of personal noise exposure than the phone microphone. A USB-C or Lightning stereo microphone (e.g. Shure MV88, Rode VideoMic Me-L/Me-C) gives spatial information. See the Microphones guide for hardware recommendations aligned with Noisecatcher's ethos.
Calibrate at the start of each session
Use the Calibration tool (tap the sliders icon on the Meter screen) to anchor your device against a known quiet environment or a reference sound level meter. A single calibration offset applies to the entire session. If you change location or device orientation significantly, re-calibrate. Log your offset value in the Notebook notes for the session.
Document what you hear, not just what you measure
The most powerful Noisecatcher record combines: the dB reading (objective), a voice note (subjective description), a pin category (contextual), and GPS coordinates (spatial). Describe what you hear in the voice note immediately after recording — the smell of exhaust, the vibration through the floor, the emotional state it produces. These details cannot be recovered later from numbers alone.
Calibration
Different devices have different microphone sensitivities, so raw dB values vary between phones. Calibration applies a fixed offset so your readings match a known reference.
Get a reference reading
Measure the same source in Noisecatcher
Apply the offset
+6.iPhone & iOS quirks
iOS has stricter browser APIs than Android. Here is what to expect on iPhone and iPad.
Microphone permission
Safari will ask once per site. If you tapped 'Don't Allow' by mistake: go to Settings → Safari → tap the Noisecatcher site → Microphone → Allow.
Compass / bearing arrows
iOS requires a user gesture to enable DeviceOrientationEvent. When you tap 'Start Measuring', the app will request orientation access. If a permission dialog appears, tap Allow. If no dialog appears (iOS 12 and earlier do not require permission), bearing tracking starts automatically.
Haptic feedback
Standard Vibration API is not available on iOS. Noisecatcher uses a workaround (toggling a native switch element) to trigger UIImpactFeedbackGenerator on iOS 18+. On older iOS versions, haptic feedback is silent — the app still functions fully.
PWA installation
To install Noisecatcher as an app: open in Safari → tap the Share button (rectangle with arrow) → tap 'Add to Home Screen'. Chrome and Firefox on iOS cannot install PWAs due to Apple restrictions.
Background audio
iOS suspends audio processing when the screen locks or the app goes to background. Keep the screen on while measuring for uninterrupted readings.
FAQ
Is this app accurate enough to use in a legal complaint?
Smartphone readings are indicative, not certified. They can support a complaint as corroborating evidence alongside other documentation (photos, videos, witness statements), and they are strong grounds for requesting an official certified measurement. They cannot alone serve as sole technical evidence in court proceedings.
Why does the dB value jump around so much?
Sound levels fluctuate naturally. Traffic, wind, voices, and environmental noise vary second to second. The 'Leq' value is more stable and more meaningful for documenting exposure over time. The '● LEVEL' stability indicator tells you when the reading is consistent enough to pin.
What is the dB(A) weighting?
dB(A) is a frequency-weighted measurement that approximates how human ears perceive loudness — lower frequencies (bass) are de-emphasised, high frequencies less so. Most noise regulation standards use dB(A). Noisecatcher applies the IEC 61672-1:2013 A-weighting curve bin-by-bin to the FFT frequency data, then sums the weighted energy to produce the final dB(A) reading. This closely matches a true A-weighted measurement; it is not a calibrated instrument, but the weighting is applied correctly.
Can I use this indoors?
Yes. Indoor measurements are useful for documenting noise intrusion from outside (traffic, neighbours, HVAC). For indoor measurements, be aware that room acoustics (reflections, reverberation) affect readings. Measure from the centre of the room where possible, not directly against a wall.
Will my data be deleted if I clear my browser history?
Yes. Pins are stored in IndexedDB; calibration settings in localStorage. Clearing site data or browser history will erase both. Export your GeoJSON file regularly as a backup.
Can I contribute my data to a shared noise map?
Yes — Noisecatcher has a built-in P2P community layer powered by Gun.js. Enable it on the map via the P2P toggle: your pins are shared in real time with nearby users without any central server. Sensitive categories (conflict, police force, harassment) require an explicit confirmation before sharing and are never shared silently. You can also export your data as GeoJSON and contribute it manually to Noise Planet (noise-planet.org) or OpenStreetMap-based noise mapping initiatives.
What is the difference between a pin and a report?
A pin is a single point-in-time reading — one dB value, one location, one timestamp. A report is a full session summary covering an entire measurement period: Leq, percentiles, noise dose, psychoacoustics, and more. Use pins to map the spatial distribution of noise; use reports to document sustained exposure over time.
How do I build a dossier for a formal noise complaint?
Create a notebook for the noise problem. Over several days and times of day, use Stop & Report to generate session reports and attach them to the notebook. Add voice notes describing what you hear and how it affects you. Drop pins on the map to show the spatial pattern. When ready, print each report to PDF and export your pins as GeoJSON. Together these form a structured, time-stamped dossier.
The microphone permission was denied. How do I fix it?
Android (Chrome): tap the lock icon in the address bar → Site settings → Microphone → Allow. Reload the page.
iPhone (Safari): Settings app → Safari → Advanced → Website Data, or Settings → Privacy & Security → Microphone → enable for Safari. Then reload.
Desktop Chrome: Click the camera/mic icon in the address bar → Always allow on this site. Or: chrome://settings/content/microphone → add the site.