> Why not just optimize for removing the gesture entirely? The microphone has to be better on a full size watch on your wrist vs the tiny ring further away on your finger.

Agreed, let the ring just be a button that can trigger recording on a watch or phone (among other tasks) rather than squeezing in a microphone and audio transmitter.

> I wonder if you could even make it perpetually powered by body heat + buffer battery if it's ONLY job was to emit a couple packets over BLE...

Neat! Or maybe a tiny solar cell? Perhaps the button itself is piezoelectric, like a wearable version of the EnOcean Nodon line of battery-free wireless switches -- a BLE advertising event costs less than 100 microjoules which a button press should be able to provide, though ensuring 100% reliability over BLE with such a tiny energy budget would be hard.

Alternately it could communicate with the watch using IR, but the knuckles might occlude line of sight. The button press could mechanically emit an ultrasonic tone, but that requires an always-on mic in the watch/phone and would be susceptible to shenanigans. Maybe pressing the button causes a specific vibration that a watch accelerometer can reliably recognize?

Now I want someone to find a way to make this work... but long term I expect that the real solution will be making hand gestures work reliably 100% of the time with no ring at all.