1. A method for determining respiration rate of a subject, comprising: receiving a photoplethysmograph (PPG) signal from a sensor comprising a light emitter and a light detector; processing, with a respiration monitor, a first data window of the PPG signal to generate one or more first respiration information signals; generating, with the respiration monitor, a first autocorrelation sequence based on the one or more first respiration information signals; identifying, with the respiration monitor, a first respiration peak segment of the first autocorrelation sequence; processing, with the respiration monitor, a second data window of the PPG signal to generate one or more second respiration information signals, wherein the second data window includes a recent portion of the PPG signal no included in the first data window and wherein the first data window includes an older portion of the PPG signal not included in the second data window; generating, with the respiration monitor, a second autocorrelation sequence based on the one or more second respiration information signals; identifying, with the respiration monitor, a second respiration peak segment of the second autocorrelation sequence; generating, with the respiration monitor, a composite peak by combining the first respiration peak segment and the second respiration peak segment; calculating, with the respiration monitor, the respiration rate of the subject based at least in part on the composite peak; and displaying, using the respiration monitor, the respiration rate of the subject on a display.