The application discloses several inventions as follows: (a) a method of monitoring consciousness of a sentient subject and automatically detecting transition states by obtaining an EEG signal and comparing the two signals to detect the transition and provide a warning signal when the transition occurs； (b) a method or apparatus for processing a non-stationary signal including segments having increasing and decreasing amplitude representing physiological characteristics of a sentient subject by performing syntactic analysis of segments, comparing height, width and error parameters of segments to identify noise segments and replacing noise segments with a straight line before classifying the signal as belonging to one of predefined sleep states； (c) a method of monitoring physiological characteristics of a sentient subject including substitution of a degraded first electrode signal by a second spare electrode signal and providing a warning signal when both signals are degraded； and (d) a capacitive or inductive element sensor for detecting the degree of opening of the eyelid including signal providing means indicative of the relative positions between a component movable with the eyelid and a reference component.
