A daily sync to upload new data from your tracker to Fitbit.com is recommended but not required.
All Fitbit trackers can record detailed minute-by-minute calorie burn and sleep data for up to 7 days, and daily steps, calories, and distance data for 30 days. For trackers that monitor heart rate, heart rate data is stored at one-second intervals during run or exercise tracking and at five-second intervals at all other times.
Fitbit Surge can store a maximum of 35 hours of GPS data. If you try to track more than 35 hours’ worth of GPS data without syncing, older data will be deleted to make room for new data. To ensure that all your GPS data is saved on Fitbit.com, sync your Surge regularly.
If you have the Fitbit software installed on your computer, when your tracker is within range of a base station (if you use an Ultra tracker) or a wireless sync dongle (for other trackers), it will automatically sync approximately every 15 minutes.