A simple clip to attach your Fitbit Flex to your watch! Now you can wear both, without crowding up your wrists. The Fitbit snaps in securely, with its lights visible, but can easily be removed for charging.
By default, it accommodates watch bands up to 28 mm wide and 5 mm thick. It's designed for the thick rubber wristband on Oakley Holeshot watches, but would fit other watches with beefy wristbands.
There is also a customizable version
here, and one with a built-in chain
as in the video below.