An apparatus and method for automatically calibrating a media sensor configured to detect advancing print media in a printing device. In some embodiments, the apparatus selects a first light intensity level and a second light intensity level greater than the first light intensity level. A light source unit, such as a light emitting diode or laser diode is activated to emit light at the second light intensity level. The light passes though print media, for example, a roll of self-adhesive labels, that is advanced along a print path of the printing device. The amount of light transmitted through the print media is measured as the print media advances. If the measured light increases, the light source unit is reactivated to emit light at the first light intensity level. In some embodiments, the apparatus identifies whether print media has changed or an out-of-stock condition exists.