Abstract: Embodiments contemplate detection, estimation, and/or adaptation to user presence, proximity and/or ambient lighting conditions. Embodiments also contemplate user proximity estimation based on input from sensors in mobile devices. Embodiments further contemplate volume control and/or audio bitstream selection based on an estimate of one or more of these parameters: user's location, age, gender, ambient noise level and/or multiple users. Also, embodiments contemplate detection, estimation, and/or adaptation to user presence and/or user attention to advertisements delivered via various mechanisms, perhaps at various locations.