Passive noise exposure tracker for your phone

A background mobile app that continuously logs ambient decibel levels throughout the day and alerts you when cumulative noise exposure crosses hearing-safety thresholds defined by NIOSH.

The idea

Most people have no idea how loud their day actually is. A noise exposure tracker runs silently in the background, sampling the microphone every few seconds, and accumulates an exposure score using the NIOSH 85 dB / 8-hour exchange-rate formula. When you cross the threshold, it notifies you. At the end of each day it logs a summary: peak level, time-weighted average, and hours spent in each decibel band.

Why build this

Occupational hearing loss is the second most common work-related illness in the US, yet most sufferers never get a warning before the damage is done. The condition is irreversible. Apps like SoundPrint exist for one-off restaurant measurements, but nothing mainstream runs passively across an entire day the way a step counter runs across your walk.

The hardware problem is solved — every phone has a calibrated microphone accurate to within a few dB for mid-frequencies. iOS 16 and Android 13 both added APIs that let background audio measurement run without keeping a full audio recording session open, which closes the battery and privacy objection that made this impractical before.

Stack sketch

React Native with Expo — single codebase for iOS and Android; Expo's expo-av handles microphone sampling.
NIOSH TWA formula implemented in a small pure-JS module with unit tests. No server needed for the core math.
SQLite via expo-sqlite — one row per 5-minute bucket: timestamp, L_eq (energy-averaged dB), peak dB.
Recharts (via react-native-svg) for the day timeline chart.
Background task via expo-background-fetch on Android; on iOS, use expo-task-manager with the significant-location-change trick to keep the process alive within platform limits.
No backend. All data stays on device. Optional CSV export via the share sheet.

Scope for v1

Sample mic every 5 seconds, average into 5-minute L_eq buckets.
Accumulate daily dose using NIOSH exchange rate (3 dB doubling, 85 dB criterion).
Push notification when dose hits 50%, 85%, and 100% of daily limit.
Today view: timeline bar chart colored green/yellow/red by exposure band.
History screen: 30-day calendar view with daily dose as a percentage.
Settings: criterion level (80/85/90 dB), working hours window to ignore nighttime ambient.
No audio is ever stored — only the computed dB number per sample window.

Out of scope for v1: cloud sync, sharing, audiologist export formats (OSHA CSV), wearable integration.

Where it could go

The most obvious next step is workplace compliance. Small construction, manufacturing, and music venue operators are legally required to monitor worker exposure but rarely can afford dedicated sound dosimeters ($200–600 each). A $5/month per-seat plan that adds a supervisor dashboard, shift-based reports, and PDF exports that match OSHA 1910.95 formatting could find genuine B2B traction — the competition is hardware, not software.

A second path is integration with wearables. Apple Watch can sample ambient sound via CMSoundLevelMeter and already shows a hearing health metric in the Health app, but it surfaces no cumulative dose. An app that reads from HealthKit, fills in gaps with phone mic data, and presents a unified daily picture could position itself as the hearing equivalent of a HRV monitor — something the biohacking/quantified-self audience would actually pay for.

Watch out for

Background audio on iOS is deliberately constrained — Apple can suspend the process at any time, so gaps in the log are unavoidable and the cumulative dose will be an undercount. Surface this limitation clearly in the UI rather than presenting numbers with false precision.