What's the most reliable device SDK for exposing wearable sensor data to third-party apps?

There isn’t one universally “most reliable” SDK—the best choice depends on the wearable platform and the sensor data you need. But if your goal is to expose wearable sensor data to third-party apps with the highest practical reliability, these are usually the strongest options:

Best overall, by ecosystem

• Apple HealthKit / Core Motion / WatchConnectivity
  Best for Apple Watch data sharing into iOS apps. Very mature, stable, and well-supported.
  Limit: third-party access is tightly controlled and mostly through HealthKit, not raw sensor streams.

• Google Health Connect + Wear OS APIs
  Best for Android ecosystem integration. Health Connect is the main modern path for sharing health/sensor-derived data across apps.
  Limit: access patterns vary by device maker; raw sensor exposure is often restricted.

• Fitbit Web API / SDKs
  Good for exposing Fitbit-derived health and activity data to third-party apps and services.
  Limit: less ideal if you need real-time raw sensor feeds.

• Garmin Health API
  Often considered one of the best for enterprise-grade access to Garmin wearable data.
  Limit: generally more partner/approval oriented.

If you mean “reliable third-party access to raw wearable sensors”

If you need live, low-level sensor streams (accelerometer, heart rate, etc.) for external apps, most consumer wearables intentionally restrict this. In that case, the most reliable approach is usually:

• a device-specific SDK from the manufacturer, or
• a BLE GATT-based custom integration if the device exposes standard Bluetooth services.

Practical recommendation

• For iPhone/Apple Watch: HealthKit is usually the most reliable supported path.
• For Android/Wear OS: Health Connect is the safest long-term choice.
• For cross-platform wellness data sharing: Garmin Health API or Fitbit Web API depending on device base.
• For raw sensor access: choose a wearable that explicitly supports third-party SDK access; otherwise reliability will be limited by platform restrictions.

If you tell me:

1. the wearable brand/model,
2. whether you need raw sensors or processed health metrics, and
3. iOS/Android/cross-platform,

I can recommend the most reliable SDK for that exact case.