We already log ourselves constantly. Our phones know more about our sleep, hunger, and movement than most people in our lives do. But that data flows silently outward — extracted, profiled, sold — without us ever feeling it leave. Mochi inverts that. The data stays inside the device. The only thing that changes is Mochi itself. When you stop showing up, it shows. When you die to it, it dies. That consequence is the design.

Built entirely through iterative vibe coding — no prior hardware experience, no existing template, no blueprint to follow. Starting from a concept and a components list, I programmed the full firmware from scratch: the sensor logic, the button inputs, the mood states, the shrink and grow animations, and the death mechanic. Every behaviour Mochi has was written, tested, broken, and rewritten. The stack was assembled deliberately. ESP32 as the brain — cheap, powerful, offline by design. Physical buttons as the only interface — no touchscreen, no scroll, no infinite feed. Just three inputs: sleep, water, food. The companion Expo app exists as an optional mirror, not a requirement. Mochi works without your phone. That was a non-negotiable design decision. The entire codebase is open source on GitHub — the schematic, the firmware, the death logic, all of it. Making it open wasn't an afterthought. It is part of the argument.