Kueki

A baby monitor that runs in the browser. Two devices, one room. The phone in the nursery listens, the phone with you plays live audio and gets a push notification when the room gets loud.

Kueki is a working prototype. Nothing is deployed yet.

Why I built it

We have phones, tablets and laptops lying around the house. Why buy another device when the ones we own already do the job? I wanted to turn a phone into a baby monitor. The apps I tried were overkill and still missed the things I cared about, and I was curious whether a progressive web app could cover it and run on anything with a browser.

It can. Kueki uses the screen wake lock, the microphone, WebRTC and web push, which is everything a baby monitor needs. I also wanted several baby devices and several parent devices in the same room, and adding one should take a single link.

Kueki was the project name of my first son while he was still in my wife's belly. It is a cute version of Küken, German for chick. He is two now and we are expecting our second, which is why I am finally building this.

What it does

• Pair any number of baby and parent devices in one room, without an account.
• Listen to several babies at once, each with its own playback control.
• Send a push notification for sustained sound, paused monitoring and disconnected baby devices, including when the parent tab is closed.
• Keep monitoring screens awake, and say so when the browser refuses.
• Set alert timing per room: how long a sound has to last, how quiet it stays afterwards, when a dropped device counts as gone, and how long activity is kept.
• Install as a PWA, follow the system light or dark appearance, dim either screen, and switch between English and German.

Kueki measures sustained sound, not whether a baby is crying. It is an extra pair of ears, not a replacement for checking on your baby.

How it works

React, TanStack Router and TypeScript on the front end, built with Vite, scripted with Bun. One Cloudflare Worker serves both the app and the API. Each room is a Durable Object with SQLite storage holding its devices, WebSocket signaling, events and queued notifications, so state survives eviction and restarts.

Live audio is WebRTC between the devices, with Cloudflare Realtime TURN as a relay when a network blocks a direct connection. No audio is recorded or stored anywhere. Push delivery goes through Apple, Google or Mozilla because the browser requires it.

Run it locally

You need Bun, Node 22 or newer for Wrangler, and the local work process manager.

bun install
bun run setup
bun run build
work up

Open http://localhost:4310/app, create a room, then open the invitation in a second browser profile and choose Baby there. Tabs in the same profile share one device identity.

Port 4310 is Vite with hot reload. Port 4313 serves the built app from dist and is what the end-to-end tests use, so rebuild before pointing anything at it. Wrangler runs the backend on port 4311 with storage under .data/cloudflare; restart it with work restart api after changing secrets.

To reach Kueki from your phones over Wi-Fi, and to deploy it to Cloudflare, see hosting. For invitations, removing access and switching rooms, see rooms.

Tests

bun run check
bun run build
bun run test
bun run test:e2e

Local CI and merging

Nobody pushes to main. Work on a branch, open a pull request, and let it merge only once the suite has passed on a real machine. Install the signoff extension once:

gh extension install basecamp/gh-signoff --pin v0.4.1

Push your branch, then run:

bun run ci

It installs dependencies, checks types, builds, runs the unit and Worker tests, starts the local Wrangler, preview and HTTPS servers, and runs the browser suite in Chromium and WebKit. It then deploys the preview Worker and repeats the deployment-shaped specs against it, so a Worker that only works under Miniflare cannot be signed off. It signs off the commit only if HEAD and the working tree still match what it tested, so every new commit needs another run. A failed run reports a red status instead. Do not call gh signoff yourself.

Merging to main is what deploys, through Cloudflare's own build.

The preview Worker

kueki-preview is a second Worker, deployed from the preview environment in wrangler.jsonc:

bunx wrangler deploy --env preview
KUEKI_E2E_ORIGIN=https://kueki-preview.assmann-568.workers.dev bunx playwright test

Being a separate script gives it its own Durable Object namespace and its own rate limiter, so the suite can create rooms and devices without touching anything kueki.app serves. It is the only environment with a workers.dev hostname; production answers on kueki.app alone. It carries no push keys, so notifications are unconfigured there.

KUEKI_E2E_ORIGIN points the browser suite at a deployment. Without it the suite runs exactly as before, against the local servers. With it, only the specs that assert nothing machine-specific run: everything in pwa.spec.ts and security.spec.ts.

The Workers test runs against real workerd and SQLite with TURN and push mocked. Browser tests drive Chromium and WebKit with synthetic microphones. TESTING.md records what has been verified on real devices and what still needs a physical phone.