Fitbit calorie burn estimates aren't 100 percent accurate, but no estimate is. Credit: Kiyoshi Ota / Bloomberg via Getty Images Most fitness trackers keep a fair number of the same stats: things ...

Fitbit is updating two of its most popular fitness trackers. The new waterproof Flex 2 and heart rate-tracking Charge 2 are available now up for preorder and will officially go on sale in the ...

Fitbit has been around since before activity tracking became cool. A wealth of experience, plenty of development and a product that's been evolving for years should mean a great result for the Flex.