A system for detecting sleep apnea, comprising: a single-wavelength PPG sensor for generating a single-wavelength PPG signal for use in detecting sleep apnea; and a processor , which is adapted to: derive heart rate variability information from the single-wavelength PPG signal; provide an estimate of respiratory effort from the PPG signal and thereby derive a surrogate respiratory effort signal; extract a surrogate feature value from the surrogate respiratory effort signal, wherein the surrogate feature value is statistically different between (i) epochs containing an end of a sleep disordered breathing event and (ii) epochs not containing such events; use body movements measured from an accelerometer or computed from body movement artifacts of the single-wavelength PPG signal, wherein the body movements are associated with arousals typically following some breathing events; and detect sleep disordered breathing events from the surrogate feature value, from the body movements and from the derived heart rate variability information and thereby distinguish between sleep disordered breathing events and normal breathing during sleep. a single-wavelength PPG sensor for generating a single-wavelength PPG signal for use in detecting sleep apnea; and a processor , which is adapted to: derive heart rate variability information from the single-wavelength PPG signal; provide an estimate of respiratory effort from the PPG signal and thereby derive a surrogate respiratory effort signal; extract a surrogate feature value from the surrogate respiratory effort signal, wherein the surrogate feature value is statistically different between (i) epochs containing an end of a sleep disordered breathing event and (ii) epochs not containing such events; use body movements measured from an accelerometer or computed from body movement artifacts of the single-wavelength PPG signal, wherein the body movements are associated with arousals typically following some breathing events; and detect sleep disordered breathing events from the surrogate feature value, from the body movements and from the derived heart rate variability information and thereby distinguish between sleep disordered breathing events and normal breathing during sleep. derive heart rate variability information from the single-wavelength PPG signal; provide an estimate of respiratory effort from the PPG signal and thereby derive a surrogate respiratory effort signal; extract a surrogate feature value from the surrogate respiratory effort signal, wherein the surrogate feature value is statistically different between (i) epochs containing an end of a sleep disordered breathing event and (ii) epochs not containing such events; use body movements measured from an accelerometer or computed from body movement artifacts of the single-wavelength PPG signal, wherein the body movements are associated with arousals typically following some breathing events; and detect sleep disordered breathing events from the surrogate feature value, from the body movements and from the derived heart rate variability information and thereby distinguish between sleep disordered breathing events and normal breathing during sleep. <EOS>