Power Reserve mode allows you to see the time of day on your Apple Watch while preserving the battery. When Power Reserve mode is engaged your Apple Watch and iPhone won't communicate and you can't access Apple Watch features including SleepWatch. In this mode, the watch will not record heart rate data either. If your battery level is too low, your Apple Watch will automatically enter Power Reserve mode.
Power Reserve is displayed on Apple Watch as a red "lightning bolt" icon:
If your Watch goes into Power Reserve mode SleepWatch will have missing/inaccurate data and you may not receive an accurate or complete sleep report.
We recommend checking the charge level of your Apple Watch prior to bedtime each night to ensure that there is an adequate charge to make it through the duration of the night.
Airplane Mode turns off wireless features on your device to comply with airline regulations. Airplane mode is enabled on your Apple watch by tapping on the icon on your home screen. SleepWatch will continue to measure in Airplane mode but will need to re-establish wireless communication to fully utilize all features. Please note, Airplane mode will need to be disengaged on both your iPhone AND Apple Watch to restore full functionality.