Google Opens Fitbit Air to Third-Party Accessory Makers
Google has released the hardware specifications and accessory design guidelines for the Fitbit Air fitness tracker to the public. The documentation is intended to enable independent designers, artisan makers, and third-party manufacturers to create custom accessories, such as bands and straps, for the device.
Technical Specifications and CAD Drawings
Google has published 2D CAD drawings detailing the Fitbit Air's sensor housing and the sleeve used by the Performance Loop Band. The CAD drawings include mating dimensions, tolerances, and force specifications for the attach and detach mechanisms.
The documentation includes three pages showing the device pod from different angles with dimensions. The official name of the device's pod is "Fitbit Pebble."
Sensor and Retention Guidelines
A Google Store page provides guidelines for accessory design, specifically regarding sensor clearance, sensor pressure, and secure retention:
Sensor Clearance: The optical heart rate and SpO2 sensors on the base of the device should remain unobstructed and maintain flush contact with the skin.
Sensor Pressure: For optimal performance during motion, sustained contact pressure of at least 35 mmHg (0.68 psi) is recommended.
Secure Retention: The tracker uses a tension-based snap-in mechanism. Accessory enclosures should follow the CAD tolerances to keep the sensor locked during movement while remaining easy to remove.
Material and Branding Requirements
Google advises using skin-friendly materials for accessories. The documentation includes a list of chemical limits, environmental standards, and testing requirements (e.g., lead-free, no PFAS).
The guidelines also include branding rules intended to avoid trademark issues.
Documentation Format
The CAD files are provided in PDF format rather than standard CAD file formats. The document includes "Google Confidential" markings and a "Not to Scale" note.
Context
The release of these specifications is similar to approaches used by other companies for their wearable devices.