Journal / Design
Why we spent two years on the inside of a ring
The outside of the bits Ring took three months. The inner surface, where the sensors meet your finger, took the rest.
A ring is the best place on the body to measure a heart at night. The finger has dense blood flow, it barely moves while you sleep, and a ring presses evenly all the way round. It is also the hardest place to put electronics, because there is almost no room and every fraction of a millimetre is felt.
Flush, not bumped
Early prototypes had sensor domes that stood proud of the inner surface. They gave strong signals and left marks on your finger by morning. We moved to a fully flush inner surface cast in medical-grade epoxy, which meant redesigning the optics so light could leave and return through a perfectly smooth window.
Three sizes of sensor spacing
A ring for a size 6 finger and a size 13 finger cannot space their sensors the same way. Every bits Ring size has its own sensor layout, tuned so the optical paths cross the same arteries regardless of how big your hand is.
What you notice
Mostly, nothing. Which is the point.