I’ve been exploring the world of modern wearable devices, but I find them lacking in a crucial aspect: battery life. To me, the ideal wearable should last for months without needing a charge. Unfortunately, the market doesn’t offer a device that fits my criteria; they come with unnecessary features and don’t prioritize what’s truly important.
So, I’ve decided to create my own. I don’t have the time to start from scratch with hardware design, but I found a potential fit in the CASIO GBD-200. However, its software isn’t up to par for my needs.
My initial plan was a tear-down to identify the microcontroller and gather necessary datasheets. The process was straightforward—easy disassembly without extra parts. But there was a setback: the microcontroller lacked any identifiable label.
Moving on to step two, I used a Nordic Semiconductor dongle and Wireshark to intercept data between the CASIO device and iOS app. While I could capture the communication protocol, it didn’t yield the firmware I sought. There were no clues about the manufacturer either.
Step three led me to explore the iOS application. By intercepting traffic between the app and CASIO servers, I aimed to uncover requests for new firmware. After some maneuvering with reverse proxy and fake Root CA certificates, I made progress. However, what I discovered was unsettling—CASIO continuously gathers analytics and data about users, which goes against my principles. This motivated me further to develop my own secure firmware for a device I wear constantly.
After some additional time, I finally obtained a significant breakthrough—a hint about the microcontroller’s name in one of the requests. This led me to a wealth of resources online: guides, datasheets, SDKs, and more. Not a bad outcome for just a couple of hours of reverse engineering.
My next steps involve defining the microchip layout and designing connectors for the available ground connectors on the watch PCB. When I have a free chunk of three hours, I plan to delve deeper. My past experience with light freeROST firmwares should come in handy for this project.