Wearable API integration: comparing SaaS, custom build, and open source

You're building a health or fitness product. You need wearable data: sleep from Garmin, recovery from Whoop, training load from Polar. At some point, you have to decide how to get that data into your product.

There are three ways to do it. Each has a different cost structure, a different engineering footprint, and a different ceiling. This article maps out all three so you can make the right call for your stage and your team.

The three approaches

SaaS vendors (Terra, Spike, Sahha, Rook, Junction) give you a hosted API layer. You connect your product to their service, and they handle OAuth flows, data normalization, and delivery. Fast to start, but you pay per user and your data lives on their infrastructure.

Custom builds mean going directly to each device provider's API and implementing OAuth, webhooks, token refresh logic, and data normalization yourself. Full control, but expensive in engineering time.

Open source (Open Wearables) is a self-hosted platform you deploy on your own infrastructure. You own the data and the code. The per-user cost is zero.

Option 1: SaaS wearable API vendors

The managed API vendor market has a handful of well-established players. Each follows the same general model: hosted infrastructure, normalized data, per-user or usage-based pricing. Here is what each one offers.

Terra API is one of the most widely adopted wearable data APIs. It covers a broad range of providers and delivers normalized data via webhooks. Pricing combines a base monthly fee with per-user charges that scale with your user count.

Spike API focuses on health and fitness data aggregation with support for wearables and health platforms. It provides mobile and web SDKs and targets teams building consumer health apps. If you are looking for a Spike API alternative, the comparison is primarily around provider coverage and pricing model.

Sahha positions itself around behavioral and mental health scoring. It derives insights from phone and wearable sensor data and offers pre-built health scores aimed at wellness and mental health products.

Rook API provides a unified API with a focus on mobile SDKs for Android and iOS. It includes a proprietary health score and targets teams building fitness and wellness apps.

Junction API is a developer-first wearable data connectivity layer. It supports a range of providers and is aimed at teams that want a lightweight integration without heavy vendor lock-in.

A full feature and pricing comparison of each against Open Wearables is available on the compare page.

Where the SaaS model breaks down

The per-user pricing model works at low user counts and breaks at scale. Most vendors charge between $0.50 and $2 per connected user per month. At 1,000 users, you are looking at $500 to $2,000 per month. At 10,000 users, the bill is $5,000 to $20,000 per month. That number compounds as you grow and never stops.

Beyond cost, there are structural constraints:

• Data residency. Your users' health data passes through the vendor's servers. For products in regulated markets (HIPAA, GDPR), your compliance posture depends on their infrastructure and their BAA terms.
• Data model lock-in. You work within their schema. Custom fields, retention policies, and derived metrics depend on what the vendor exposes.
• Vendor dependency. Pricing changes. Provider contracts change. Services shut down. Your switching cost is high.
• Health scoring opacity. Most vendors offer a small number of fixed health scores with no visibility into how they are calculated.

When it makes sense

SaaS vendors are the right starting point when you are pre-product-market-fit, have fewer than 1,000 users, and need to validate whether wearable data is even valuable in your product before investing engineering time.

Option 2: Building direct integrations

Some teams skip the vendor layer and build integrations directly against each provider's API.

You own the code, the data model, the storage, and the logic. No per-user fees, no vendor dependency.

What it actually costs

A production-grade integration with a single provider takes a senior backend engineer two to four weeks to build properly: OAuth implementation with token refresh and error recovery, webhook infrastructure, rate limit management, and data normalization.

Each provider has its own quirks. The Garmin API uses OAuth 1.0a and a push-based delivery model. The Whoop API uses rotating refresh tokens. The Strava API requires webhook deduplication. The Apple Health API has no REST endpoint at all and requires a native iOS SDK. Google Health Connect and Samsung Health both require Android-side implementation with background sync.

After four weeks, you have one integration. A product that needs Garmin, Whoop, Polar, and Strava has committed four to eight months of backend engineering to infrastructure that has nothing to do with what makes your product different. Provider API updates add ongoing maintenance on top of that.

When it makes sense

Building direct integrations makes sense when you need a single, deep integration with one specific provider and have the engineering bandwidth to own it long-term. A multi-provider health platform is not a good fit for this approach.

Option 3: Open source with Open Wearables

Open Wearables is a self-hosted open-source platform for wearable health data integration. You deploy it on your own infrastructure, and it handles provider integrations, data normalization, and health scoring across all major wearable platforms.

Open Wearables supports live integrations with all major wearable platforms. The full list of supported providers is available at openwearables.io/integrations.

One normalized API schema regardless of source. Token lifecycle management, webhook handling, and provider-specific complexity are handled by the platform.

Health scoring and AI

On top of raw data, Open Wearables computes open health scoring algorithms: sleep, recovery, strain, HRV, resting heart rate trends, energy, and VO2 max. Every algorithm is published and auditable. You can adjust thresholds for your population or customize scoring for clinical vs. fitness contexts.

For teams building AI-powered features, an MCP server connects your LLM directly to the health data layer, enabling trend detection, anomaly flagging, and cross-metric reasoning.

Cost and compliance

At 10,000 users, a SaaS vendor costs $5,000 to $20,000 per month. Open Wearables costs only what your infrastructure costs. Deployment is Docker Compose or one-click Railway. The quickstart gets you to a first API call in under five minutes.

Data stays on your servers. You control where it lives, how long it is retained, and who has access. HIPAA-eligible infrastructure and BAA support are available through the enterprise tier.

If you want help

Open Wearables is built and maintained by Momentum, a healthtech software studio with 10 years of experience building health products. If you want a team to handle deployment, custom provider integrations, or bespoke health scoring for your use case, that is what we do. See the pricing and support options for details.

Side-by-side comparison

SaaS Vendor

• Time to first data: Hours
• Per-user fee: $0.50-$2/mo
• Cost at 10k users: $5k-$20k/mo
• Data ownership: Vendor's servers
• Multi-provider support: Yes
• Health scores: 0-5, black box
• Score customization: No
• AI reasoning: Limited / varies
• Source code: Proprietary
• Compliance (HIPAA/GDPR): Depends on vendor
• Vendor lock-in: Yes

Custom Build

• Time to first data: Months
• Per-user fee: $0
• Cost at 10k users: Engineering time
• Data ownership: Yours
• Multi-provider support: Build each one
• Health scores: Build yourself
• Score customization: Yes
• AI reasoning: Build yourself
• Source code: Internal
• Compliance (HIPAA/GDPR): Full control
• Vendor lock-in: No

Open Wearables

• Time to first data: 5 minutes
• Per-user fee: $0
• Cost at 10k users: Infrastructure cost only
• Data ownership: Yours
• Multi-provider support: Yes
• Health scores: Open algorithms
• Score customization: Yes
• AI reasoning: MCP server for any LLM
• Source code: MIT licensed
• Compliance (HIPAA/GDPR): Full control
• Vendor lock-in: No

How to choose

• Start with a SaaS vendor if: you are pre-product-market-fit, have fewer than 1,000 users, and need to validate the product before investing in infrastructure.
• Build direct integrations if: you need a single deep integration with one specific provider and have the engineering bandwidth to own it long-term.
• Use Open Wearables if: you are past initial validation, need multi-provider support, care about where your users' health data lives, or need health scores that are auditable and customizable.

Getting started

Open Wearables is available on GitHub under the MIT license. The quickstart covers deployment and your first API call.

If you want to talk through your specific architecture before making a decision, book a demo.