US9192326 illustrates a sleep monitoring system that can be embodied within a wearable device or in a mobile device. The system includes an accelerometer to monitor a user's movements. The system determines when the user is falling asleep into a sleep session based on the user's movements. The system also identifies the sleep session as a power nap or a longer sleep based on a current time of day, a time since a last longer sleep, and a location of the user. The system notifies the user to change the user's location when the user falling asleep would have a negative effect on the user. When the user falling asleep does not have a negative effect on the user, the system determines a time to wake up the user based on a combination of the current time of day, the time since a last longer sleep, the location of the user, user preferences, and measured information regarding the sleep session.