This is indeed a good study. I recently experienced one such thing. I bought fitness tracker which I used to monitor my sleep quality. I paired it to smartphone and kept phone aside and slept wearing the tracker. This activity I repeated for entire week and I found that my sleep quality over the week exacerbated compared to time when there was no tracker. When I thought over this, I found out that when I was sleeping wearing the tracker, I was subconsciously thinking continuously about how my sleep quality will be, how will be my heart-rate during sleep, it should always be in resting zone, etc... I had all sorts of kinda unnecessary apprehensions/ worries. This was OK for a day or two... then I got used to the tracker, still my quality of sleep was poor for remaining week. When I further thought over this, it appeared to me that I had setup a goal for daily 6 hour sound sleep and I have to achieve that. I had subconscious pressure to achieve that goal which is making me restless frequently. Atlast I gave up experiment of sleep monitoring and now I can sleep peacefully without tracker. :-)