A method for determining the signal quality of samples in a physiological signal, in particular an electrocardiogram (ECG) signal, is provided. A supra-threshold sample sum, a noise threshold crossing sum, or both are calculated in a noise detection window including the sample to be evaluated, and low signal quality is indicated if either or both of the sums exceed respective values. ECG beat detections can then be labeled as unreliable based on the determination of low signal quality for one or more samples between the detections.
