Logged deep sleep when I was awake and exercising

[jonaf]

My sleep status from last night shows that I had deep sleep for one and a half hours before I went to bed. The rest of the night I had a number of  awake periods that I did not have.  On several occation the device does not start logging my sleep until several hours after I fall asleep. 

How shall I trust the loggings regarding the other data from the fitbit when it is making up false readings about my sleep?

[RiekoC]

Hello @jonaf 

Health trackers use movement and heart rate to record users sleep stage. How this works is explained in What should I know about Fitbit sleep stages 

How does my Fitbit device automatically detect my sleep stages?

Sleep stages are traditionally measured in a lab using an electroencephalogram to detect brain activity along with other systems to monitor eye and muscle activity. While this method is the gold standard for measuring sleep stages (source), your device can estimate your sleep stages in a more comfortable, convenient way.

Fitbit estimates your sleep stages using a combination of your movement and heart-rate patterns. When you haven’t moved for about an hour, your tracker or watch assumes that you’re asleep. Additional data—such as the length of time your movements are indicative of sleep behavior (such as rolling over, etc.)—help confirm that you’re asleep. While you’re sleeping, your device tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV), which fluctuate as you transition between light sleep, deep sleep, and REM sleep stages. When you sync your device in the morning, we use your movement and heart rate patterns to estimate your sleep cycles from the previous night.

It helps to understand that sleep data from a health tracker is not as accurate as using a device that is designed to track sleep stages, such as an ECG. However, the trackers do help provide an indication of a user's sleep pattern. 

If you want to know which health trackers have the best performance for sleep tracking, you might want to check out The Quantified Scientist YouTube channel. He evaluates various health trackers using scientific equipment to determine their accuracy for various stats. 

[jonaf]

I had indeed moved during the the time I am referring to. I was exercising the last hour before I went to bed. And yes, I was wearing the fitbit that logged this as deep sleep. I do not trust the data it records.