> ## Documentation Index
> Fetch the complete documentation index at: https://openwearables.io/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Wearable Sync SDK

> Native mobile SDKs for background sync from Apple HealthKit, Samsung Health, and Health Connect. iOS, Android, Flutter, and React Native supported.

## Introduction

Open Wearables Sync SDKs enable seamless background synchronization of health data directly from **Apple HealthKit** (iOS), **Samsung Health**, and **Health Connect** (Android) to the Open Wearables platform.

Unlike cloud-based providers (Garmin, Polar, Suunto) that use webhooks and OAuth, on-device health stores require a **push-based model** where data is sent from the user's device to your backend.

<Note>
  **Why Push-Based?** Apple HealthKit, Samsung Health, and Health Connect don't expose cloud APIs. Health data lives exclusively on the user's device, so the mobile app must actively push data to your backend.
</Note>

## Architecture Overview

<Steps>
  <Step title="Health Data Store" icon="heart-pulse">
    Health data is stored locally on the user's device — in Apple Health (iOS), Samsung Health, or Health Connect (Android).
  </Step>

  <Step title="Your App + Sync SDK" icon="mobile">
    The SDK reads data from the health store and handles background synchronization automatically. Available as native iOS (Swift), native Android (Kotlin), or Flutter (cross-platform).
  </Step>

  <Step title="Open Wearables Platform" icon="cloud-arrow-up">
    Data is pushed to `POST {host}/api/v1/sdk/users/{userId}/sync` and normalized to the unified data model.
  </Step>
</Steps>

## Key Features

<CardGroup cols={2}>
  <Card title="Background Sync" icon="rotate">
    Health data syncs automatically even when your app is in the background, using iOS Background App Refresh or Android WorkManager.
  </Card>

  <Card title="Incremental Updates" icon="bolt">
    Uses anchored queries to sync only new data since the last sync, minimizing battery usage and network traffic.
  </Card>

  <Card title="Secure Storage" icon="shield">
    Credentials stored securely in iOS Keychain or Android EncryptedSharedPreferences. API keys never leave your backend.
  </Card>

  <Card title="Wide Data Support" icon="chart-line">
    Steps, heart rate, workouts, sleep, body measurements, nutrition, and more — all normalized to Open Wearables data model.
  </Card>
</CardGroup>

## Available SDKs

<CardGroup cols={3}>
  <Card title="iOS (Swift)" icon="apple" href="/sdk/ios">
    Native iOS SDK — the core implementation for Apple HealthKit sync.
  </Card>

  <Card title="Android (Kotlin)" icon="android" href="/sdk/android">
    Native Android SDK — sync from Samsung Health and Health Connect.
  </Card>

  <Card title="Flutter" icon="mobile" href="/sdk/flutter">
    Flutter SDK — cross-platform wrapper around the native iOS and Android SDKs.
  </Card>

  <Card title="React Native" icon="mobile" href="/sdk/react-native">
    React Native SDK — cross-platform wrapper around the native iOS and Android SDKs.
  </Card>
</CardGroup>

## Security Model

The SDK uses a secure token-based authentication flow that keeps your App credentials safe:

1. **App credentials stay on your backend** - `app_id` and `app_secret` are never exposed to mobile apps
2. **Short-lived access tokens** - Generated server-to-server via `POST /api/v1/users/{user_id}/token`, forwarded to the mobile SDK
3. **Secure credential storage** - iOS Keychain / Android EncryptedSharedPreferences
4. **Automatic token refresh** - SDK can automatically refresh expired tokens using the `refresh_token`
5. **API key auth** - Alternative for internal tools (not recommended for production)

<Warning>
  **Never embed your `app_id` / `app_secret` in your mobile app.** Always generate access tokens on your backend and pass only the tokens to the mobile SDK.
</Warning>

## Next Steps

<CardGroup cols={3}>
  <Card title="iOS SDK" icon="arrow-right" href="/sdk/ios">
    Get started with the native iOS SDK (Swift)
  </Card>

  <Card title="Android SDK" icon="arrow-right" href="/sdk/android">
    Get started with the native Android SDK (Kotlin)
  </Card>

  <Card title="Flutter SDK" icon="arrow-right" href="/sdk/flutter">
    Get started with the Flutter SDK
  </Card>
</CardGroup>