Sleep tracking on the Flex 2 seems relatively accurate and because of the small size of the activity band it's far more comfortable to wear to bed at night. (digitaltrends.com)
If you do wear it to bed, you'll be asked to set the total number of hours you'd like to sleep at night. (digitaltrends.com)
Sometimes I even wear it to bed just because it's so warm and soft. (garnethill.com)