A method is provided for determining contact of a sensor with a patient's tissue. The method comprises comparing the intensity of detected light at a first wavelength to a threshold, wherein the first wavelength is not used to determine a physiological characteristic of the patient, and determining if the sensor is in contact with the patient's tissue based on the comparison. In addition, a method is provided for determining the amount of light shunting during operation of the sensor. The method comprises comparing the intensity of detected light at a first wavelength to a threshold, wherein the first wavelength is not used to determine a physiological characteristic of the patient, and determining the amount of light shunting based on the comparison.