A method and apparatus are provided for authenticating a measure of sleepiness in a person in which a measure of the person's sleepiness and an authentication step are performed substantially simultaneously on substantially the same physical attribute of the person. In one form, an eye of a person is scanned under infrared light and a unique identifying code is calculated from the iris as an authentication step. In one form, a measure of the person's sleepiness is determined from changes in the pupil size with time.