Hi Joumana, the Bio2 and Fusion2 utilize auto-sleep tracking - all you need to do is wear your tracker when you sleep. We do recommend syncing the tracker with the app after sleep is tracked - simply double tap the tracker with the app open to prompt a sync. There can be a delay between syncing data to the app, data being transferred to our servers, and data being displayed on the app home screen. Make sure you're connected to a reliable Wifi/cellular data signal when syncing.
Auto-sleep tracking is based on motion. There is a time delay (roughly 20-25 minutes of little to no registered movement) before sleep begins to track. There is an auto-exit function in place as well, which is triggered based on tracked motion being analyzed as the tracker progressively transmits data to our servers.