JanVaani — जनवाणी

Offline-first P2P alert mesh for civilians during internet blackouts. No internet. No server. No central point of failure.

Built for 418 Hackathon 2026 — Web Development Track.

What it does

• Share emergency, medical, food/water, safe-route, and missing-person alerts with people nearby — with zero internet.
• Alerts propagate hop-by-hop across devices and physical locations.
• Each message is cryptographically signed with an ephemeral Ed25519 key.
• Alerts expire automatically (TTL). One-tap panic wipe destroys all local data.

Three transport layers

Transport	When it works	Range
BroadcastChannel	Same device — multiple browser tabs	Instant
WebRTC + hotspot	Nearby devices on shared LAN	~50 m
QR handoff	Physical scan — fully air-gapped	1 m

The system degrades gracefully. If WebRTC fails, QR still works. If there is no hotspot, three tabs on one laptop still demonstrate full A→B→C propagation with real hop counting.

Features

• Local alert creation with 6 categories
• QR share — animated multi-frame for large payloads (pako compressed)
• QR scan — import alerts from any device
• WebRTC gossip mesh — SYNC_HASHES → diff → SYNC_ALERTS → SYNC_DONE
• BroadcastChannel mesh — zero-setup multi-tab sync
• Community chat over WebRTC data channel (persisted to IndexedDB)
• Local news broadcast screen
• Village Board poster — printable QR for physical notice boards
• Ed25519 signing — alerts signed with ephemeral per-device keypair
• TTL expiry with fresh/aging/expiring/expired visual states
• Hop badge — 📡 N visible on every relayed alert
• Panic wipe — one tap deletes all local data
• Shake to wipe — physical gesture triggers panic wipe
• PWA — installs offline, service worker caches all assets
• Hindi (हिंदी) and Telugu (తెలుగు) language support

Run locally

npm install
npm run dev
# Opens https://localhost:5173
# Accept the self-signed cert warning on every demo device

Demo — A → B → C propagation (3 browser tabs)

1. Open https://localhost:5173 in three browser tabs
2. In Tab A: Create an Emergency alert
3. Watch Tab B receive it with 📡 1
4. Watch Tab C receive it with 📡 2

No hotspot. No QR. No setup. BroadcastChannel connects the tabs instantly.

Demo — Real cross-device (3 phones)

1. Phone 1 enables mobile hotspot (no SIM data needed)
2. Phones 2 & 3 join the hotspot and open https://PHONE1_IP:5173
3. Accept the cert warning on each phone
4. Phone 1 → #connect → choose Share (A) → QR appears
5. Phone 2 → #connect → choose Receive (B) → scan QR → sync
6. Phone 2 → repeat as Share (A) with Phone 3 as Receive (B)
7. Phone 3 shows the original alert with 📡 2

Security model

• No account. No login. Ephemeral Ed25519 keypair generated per device, stored only in localStorage. Fingerprint shown as XXXX-XXXX.
• Each alert carries a detached Ed25519 signature and the sender's public key.
• Loss of one device exposes only the alerts stored on that device — not the full network.
• Panic wipe: Settings → Clear All Data. Deletes IndexedDB + localStorage.

Stack

Vite · vite-plugin-pwa · idb · pako · tweetnacl · qrcode · html5-qrcode · Vanilla JS (no framework)