Provided herein are methods and devices configured to detect the heart rate of a user. The method includes receiving at least one input signal, separating the input signal into signal components, receiving a motion signal from the user, and applying a Bayesian filter to the signal components and the motion signal to estimate the heart rate of the user. The method further includes calculating a combination of at least two reflected light signals from at least two different wavelengths. The device includes a photodetector configured to detect at least one reflected light signal resulting from the emitted at least two different wavelengths and a motion detector for detecting a motion signal. The device also includes a processing component configured to calculate a combination of the reflected light signals, separate the combination of detected light signals into signal components, and apply a Bayesian filter to the signals.