Technical architecture

Three tiers

Bracelet  ── BLE ──>  Phone app  ── HTTPS ──>  Cloud (optional)
   ↓                     ↓                          ↓
8 sensors           Personal model              Aggregated stats
On-device ML        WVI compute                 Encrypted backup
14-day buffer       Direction pick              Web dashboard

Bracelet

C firmware on Zephyr RTOS. ~80 KB main app. OTA updates over BLE.

Phone

Native iOS (Swift / SwiftUI) and Android (Kotlin / Jetpack Compose). Local model in CoreML / TFLite. Local SQLite for daily summaries; raw streams kept on encrypted device storage.

Cloud

A small Rust service deployed in the EU (Frankfurt). PostgreSQL with per-user envelope encryption. No raw biometric streams ever stored. No third-party analytics SDKs.

Security boundary

The trust boundary is the phone. Raw streams stay phone-side. Daily summaries cross the boundary only if the member opts in, and only encrypted under the member's key.