You have a Fitbit? That's great! Besides tracking activity, most of the Fitbit devices will also track your sleep activity.
All Fitbit devices track sleep automatically (except Fitbit Flex and Fitbit One). Simply wear your device to bed. Once your tracker syncs with your account, you will be able to view your sleep stats under the "Tracking" menu, by clicking on "Stats" and scrolling down to the section labeled "SLEEP".
To learn more about how to track sleep with your Fitbit Flex and Fitbit one, click here.