I never liked talking to my phone in public. Pull it out, unlock it, wait for the assistant to wake up, wait for it to understand and execute : it kills the whole point of a voice command being quick. I wanted the opposite: press a button on my wrist, talk, done. No screen lighting up, no activation needed.
So I built Voice Band. It's a XIAO nRF52840 Sense, a 110 mAh cell and a button, in a 3D-printed case small enough to wear. Hold the button, talk, let go. The board records on its onboard mic, compresses the audio, and ships it over BLE to a phone app that handles the transcription and actually fires the action — a timer, a text, a quick note.
The part that ate most of my evenings was moving audio across BLE without blowing the power budget. Raw 16 kHz PCM is too fat to stream comfortably over a Nordic UART link, so it gets IMA ADPCM compressed 4:1 on the board first, wrapped in a small header I called CVOX. Even then I spent a while chasing buffer overruns when the recording outran what the link could drain. Push-to-talk turned out to be the right call for more than privacy: the board only wakes on a press and drops to around 0.4 µA the rest of the time, so a tiny battery lasts a genuinely long while.I also spent a lot of time on the app itself: making the assistant smart and understanding.It's not a product. It's a prototype and the firmware is open if you'd rather flash your own XIAO and build one. The band does exactly one job: catch your voice and get it off your wrist cleanly. The phone does the rest
Feel free to add functionalities with the onboard IMU for example : step counting, sleep tracker, etc
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