I have been using my FitBit Flex since late April now, and it has been a mostly great experience. Unlike my old FitBit Ultra (which I ultimately lost) I don’t have to worry about losing it because I wear it on my wrist. I also don’t worry about forgetting it in the morning because I sleep with it on each night in order to track my sleep. The data is provides is great, and particularly useful for someone like me, who enjoys playing around with the data.
But I did say I was mostly happy. There have been three problems, both of which have been corrected, but which I wanted to mention here in case anyone else has experienced these problems.
1. Sudden drop in step count, despite the same amount of walking
Not long after I got my Flex, I upped my daily goal to 15,000 steps/day. At first, I had a little difficulty meeting this goal, but once I began spending my entire lunch hour walking, it became routine not just to meet, but to exceed this goal on a regular basis. A typical week of walking looked like this for me:

A few weeks later, beginning around June 23, I noticed a sizable drop off in the step count for the week:

Set aside the two days at the end of the week when we were driving up to Maine and I was in the car for most of the day, doing very little walking. What is odd about this week is that my step counts are down across the board, never even reaching 15,000 steps.
But the strangest thing of all is that I was taking the same 3 walks I do every day. I was not walking any more, but I was not walking any less. So why the lower counts?
Take a look at the data for Tuesday, June 5:
You can clearly see the steps for my three walks. You can further see that each time, they reach nearly 600 steps for the time interval shown, which I think is 5 minutes. Now take a look at the data for exactly 3 weeks later, the week in which I noticed lower step counts:
You can still see all three of my walks, but you’ll note that they barely reach 500 steps/interval, despite the fact that I tend to walk at the same pace and the same distance each time. For some reason, my Flex was under-reporting steps.
Of course, it could have been over-reporting for all of the other weeks, but since this week was the exception, I decided that it was under-reporting.
I tried a number of things, none of which seemed to make a difference, including resetting the device. We’ll come back to this shortly. First…