Size 4.0mm hook, or appropriate size depending on how loose your tension is
Small amount of worsted yarn (leftover scraps will do)
At the end of row 10, sl into next two stitches (I found that the start of the round migrates and this was to make the seam of the pocket align with the edge of the band). The pocket should measure about 2" and be longer than the Fitbit once inside. Try it out before continuing.
Row 1: Ch 2, DC in same stitch, DC in next 3 stitches. (2 chain stitches +4 DC)
Row 2: Ch2, turn, DC 4.
Repeat row 2 until the band is a snug fit on your wrist, the DC will stretch. For me, 11 rows of DC was perfect.
The Ravelry page featuring this pattern can be found here: http://www.ravelry.com/patterns/library/fitbit-one-or-pocket-wristband-2