Materials:
4.0 (size 6) double pointed knitting needles (or go down a size if you tend to knit more loosely. I am a tight knitter!)
Small amount of Worsted yarn (I used leftover scraps)
Yarn needle
Long tail CO 10 sts.
K1P1 rib in the round until the pocket measures a little longer than the Fitbit (without the case). Mine was about 2 inches.
Then, divide the stitches evenly on 2 needles and knit the 2 rows as one to close the pocket, which is known as a 3 needle bind off.
Knit the band (5 sts) in garter stitch until it is the right length for the wristband, keeping in mind that it will stretch out a bit once you try it on. I stretched mine out a little first so it fit a little more snug.
BO and use the tail of the yarn to sew the BO edge to one side of the pocket opening. The band can be worn with the opening on the inside to prevent the Fitbit from falling out, but it isn't necessary. It stays in pretty well as long as the pocket fits snugly over the Fitbit.
The Ravelry pattern page featuring this pattern can be found here: http://www.ravelry.com/patterns/library/fitbit-one-or-pocket-wristband
