My most reliable fit wearable so far has been my Wii U Fit Meter. It's about as smart as a Tamagotchi, but it gets the job done for me. Data xfer via IR instead

My most reliable fit wearable so far has been my Wii U Fit Meter. It's about as smart as a Tamagotchi, but it gets the job done for me. Data xfer via IR instead of radio. CR2032 battery goes for a few months. I find it a clever balance of cheap tech and engineering trade-offs - very Nintendo in that regard.