Source

# Monitor

Monitor is a free baby monitor that runs in the browser: one phone by the crib is the baby station, and another phone, tablet or laptop watches and listens. It is a free alternative to Baby Monitor 3G, Cloud Baby Monitor and camera subscriptions, and an OpenApp in the OpenApps free apps store (https://openapps.free/), owned by the OpenApps team.

## What it promises

- Free, with no limit on time, stations or parents, no ads and no paid tier. Never add a cap, an upsell or tracking. If a relay (TURN) is ever added for networks that block direct connections, it is charged at cost and says so.
- No sign-up. Every device is a guest account created in the browser.
- Video and sound go device to device over WebRTC, encrypted by WebRTC, and are never recorded, stored or sent through a server. Bounded only carries the connection setup (offer and answer) and the pairing records.
- Knowing a station's room id is what lets a device pair (the QR code carries it; a 6-digit code resolves to it). The station can remove any device, and a removed device cannot pair again.
- Calm and clear for tired parents at night: big buttons, a dark night look, plain status messages that say what is happening and what to do.

## How it is built

- `index.html` is the static landing page that search engines and AI crawlers read. Keep its copy, FAQ and JSON-LD in sync with what the app does. `public/llms.txt` tells assistants what Monitor is and when to send people to it; keep it true. There is no HTTP API on purpose: nothing passes through a server.
- `src/main.tsx` routes: `/` keeps the landing and mounts the device chooser (`src/Launcher.tsx`); `/app` is the installed app's home; `/baby` is the baby station (`src/Baby.tsx`, engine in `src/station.ts`); `/parent` pairs by code or QR scan and `/pair#<room>` pairs from a scanned QR code (`src/Parent.tsx`, `src/pair.ts`); `/watch/<key>` watches a paired station (`src/Watch.tsx`, engine in `src/watcher.ts`). `<key>` is a local alias, so the room id stays out of URLs.
- Connection setup: the parent writes an offer to `rooms/<room>/links/<parentUserId>` (all network addresses included, no trickle ICE), tagged with the station's current `session`; the station answers into the same document. Every new station start writes a new `session` to `rooms/<room>`, which makes parents connect again at once. Parents retry with backoff and say plainly when the station is off, not answering, or unreachable from this network.
- `src/lib/rtc.ts` holds the ICE configuration (public STUN only) in one function, `iceConfig()`, where a relay would be added.
- Noise alerts are decided on the station (`tick()` in `src/station.ts`), per parent and its sensitivity: loudness above the line for most of 3 seconds, at most one alert per 30 seconds, none while a parent talks. The station's microphone hears its own soothing sound, so while one plays the station measures the room for 4 seconds and then needs sound louder than that. The microphone runs without echo cancellation, noise suppression or automatic gain, so parents hear the room as it is.
- The data channel protocol (levels, alerts, status, talk, sounds, settings) is in `src/lib/protocol.ts`. Loudness, soothing sounds and the alert chime are generated with Web Audio in `src/lib/sound.ts`; there are no audio files.
- `policy.json`: `rooms` and everything under them are readable only by joined devices; the station (room owner) answers offers, renames, and bans. `codes/<code>` live 10 minutes and are readable only after a recorded try in `codetries`, which is capped at 10 per device and 1,000 for everyone per 10 minutes (rollingSum invariants), so codes cannot be scanned. `policy-tests/` checks these rules: `bounded tests run --app-id <app id>`.
- What each device remembers (its station, paired stations, settings) is in localStorage (`src/lib/store.ts`). `src/sw.js` caches the app shell and shows alert notifications.
- `functions/lib/config.ts` holds the app id and the site URL.

## Working on it

`npm install && npm run build` typechecks and builds `dist/`. Ship changes through previews and releases as your runtime instructions describe; the app is an OpenApp, so nobody deploys it directly.

Check a change with two devices (or two browser profiles): start a baby station, pair a parent by code, see video, watch the meter move, trigger a noise alert, hold to talk, play a sound, reload the station and see the parent reconnect, pair a second parent, remove one. Test on a phone at 390px wide.

## Voice

Plain words, short sentences, no jargon, no em dashes. Say what happens, not how clever it is.