Those FitBits are nifty and all but what most guys don't seem to realize is that they can get you caught by your SO.
If your wife happens to look at your data, she's gonna notice something fishy and start wondering why your activity levels seem to peak at strange times of the day. This especially goes for the guys who go see a girl on their lunch breaks. Nothings more suspicious than your heart rate going 160 when you're supposed to be sitting on your butt all day.
So yeah, either find a way to turn it off without being noticed, or take it off before a session.
Hope this helps.
Honey Davis