Garmin Fenix tricked into reading external efficiency metrics

Garmin offers a comprehensive ecosystem. It is not an entirely open one, even though certain steps have been taken to make it more accessible. For example, users cannot just pair any sensor with a Garmin smartwatch to display metrics such as running efficiency. This might be less relevant for end users, but potentially significant for makers.

A programmer has now succeeded in sending data to a Garmin Fenix ​​(available at Amazon) using an ESP32 or nRF52832 chip, which the Fenix ​​smartwatch recognized as native data. Specifically, these are running efficiency metrics, namely ground contact time and vertical oscillation. Sample data was used for this, not actual data collected by a fully functional DIY sensor.

Both the detailed Reddit post and the two blog entries are definitely worth reading, as they also explain how the development process unfolded. Sam Dumont used Claude as a tool and, by his own account, needed this assistance because he lacks expertise in Bluetooth Low Energy and reverse engineering, though he has been familiar with the Garmin platform and its quirks since 2020. The post demonstrates how Claude can apparently be put to good use in programming as a technically savvy colleague who critically examines one’s own ideas and may offer new approaches. According to Dumont, however, a basic understanding of technology is still necessary.

Of course, it remains unclear to what extent this project will be adopted by other developers. In the long run, the project, which Sam Dumont also shared via GitHub, could certainly open up opportunities for other makers.