I purchased this last week and have have worn it for around 7 nights. So far it has successfully tracked sleep 3 out of those 7 nights, that's about 42% or the time. The last 2 nights, it has tracked sleep 0 times. This is leading to all metrics now being incorrect, since there is no HRV, no Sleep score, etc. So all of my training metrics are now completely inaccurate. Seriously how can a device with one single purpose work so poorly. Because of the cascading effect this data has on the overall metrics, it's back to wearing my watch for me.