A sleep monitoring application is installed on a mobile device. The mobile device is placed in a location when a user sleeps and records environmental sound. The sleep monitoring application determines indicators of sleep activity such as breathing sounds made by the user, and determines a sleep state of the user based on the indicators of sleep activity. Sleep disorders can be detected from the indicators of sleep activity. The sleep monitoring application may generate a report that summarizes the user's sleep states and alerts the user to any sleep disorders. The sleep monitoring application can use the environmental sound and the determined sleep states to determine ambient sound that is associated with good sleep. Later, if the sleep application determines the user is having problems sleeping, the sleep monitoring application can play the determined ambient sound to help the user sleep.