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It may happen that your fitbit flex isn’t tracking, or responding normally or lights stay on and you need to reset or restart the device. This video shows you how.
1. Put your tracker portion of the fitbit flex into the charging cable and plug it into the USB port.
2. Take a paperclip, flip the charger upside down so that you can see the pin hole towards the cable side of the charging cable.
3. gently press the paperclip into the hole and hold for 3-5 seconds, then release.
The fitbit flex will restart and you will see a short LED light show.
Note that your tracking data isn’t erased when doing this.