https://thetinypod.com/

I would actually love something like this as a new iPhone mini.

Vaguely related— where is the Apple Watch Mini? It seems like they’ve explored expanding the capabilities of the watch form factor with the Ultra, but it would be interesting to see how a minimalistic fitness tracker only experience would resonate with customers.

Smart rings seem like the closest example that comes to mind, but it seems like you are limited by the data you can capture from that region of the body relative to the whole. Maybe some kind of minimal glove?