Detecting a primary user of a device

A device may identify a user among multiple individuals detected by comparing a physiological condition, such as a heart rate, of the multiple detected individuals as detected by a camera of the device with a physiological condition of a user of the device using different sensors. A heart rate may be detected by a camera by monitoring blood flow to an individual's face. A heart rate may be detected by a motion sensor by monitoring vibrations of the device that are in an expected frequency range. If a heart rate of a user matches a heart rate of an individual seen by a camera, that individual may be determined to be the user of the device. The position of the individual may be used to then render a user interface.