The present invention monitors a physiological process intrinsic to humans and which measures directly the approach of a sleep state. When sleep onset is detected, the subject is restored to a fully awake state by an alert mechanism. Sleep onset is determined by monitoring EEG and EMG signals of the subject with a bispectral index monitor and applying an analysis algorithm to the index values output by the monitor. As a person tires, the value of their bispectral index begins to drop and then oscillate back and forth between two discrete levels. This pattern is consistent among various subjects and indicates an early warning of impending sleep, before a dangerous loss of vigilance has occurred.
Alarm upon detection of impending sleep state