I wear a Fitbit on one wrist - needs charging every 9-10 days, and a "dumb" automatic watch on the other - never needs winding, just a tweak every month. I use a chest band HRV on the rower (more accurate than the FitBit, IME), but its connection with my Garmin head unit is spotty, so I usually don't bother with the chest band on the bike.