Sensor Watch is a bridge between eras. It takes an iconic 30-year-old design from a golden age of digital watches, and pairs it with a modern, powerful microcontroller and state-of-the-art sensing capabilities. This small circuit board, less than an inch in diameter, replaces the original quartz movement in a Casio F-91W or A158W watch to put the capabilities of an ultra-low-power ARM Cortex M0+ microcontroller on your wrist.

Photo: the Sensor Watch circuit board next to a Casio F-91W

Sensor Watch is both an open source hardware project and a product available for purchase, as well as an attempt to launch a hardware platform from scratch:

Along the way I generated copious amounts of documentation, including a Watch Interface Guidelines document (like Apple’s HIG) talking through the unique UX considerations associated with the simple display, limited inputs and low power requirements. I also did marketing, copywriting and web design for the project.

As of September, I am on track to ship the remaining boards by the end of 2022.


Sensor Watch borrowed its board outline from Pluto, an F-91W board swap from carrotIndustries. It was also deeply inspired by Travis Goodspeed’s Goodwatch. Finally: I learned of the SAM L22 microcontroller, which makes this whole thing possible, from Greg Davill’s arm-watch; his Advent Calendar of Making in December of 2020 directly inspired me to design Sensor Watch in January of 2021.

Sensor Watch would not exist but for these open hardware projects. Thank you all!