The Withings Go is a small and light fitness tracker that can be worn as a wristband or clipped to a clothing, and it features a circular E Ink display. The Go monitors activity and sleep, is water resistant (50 meters) and can monitor swim strokes.

Withings Go photo

The Go will ship in Q1 2016 for $69.

E Ink display info: 
Circular E Ink display
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ynvisible ink kit - create your own electrochrommic printed displaysynvisible ink kit - create your own electrochrommic printed displays