A wearable cardioverter defibrillator system, comprising: a support structure configured to be worn by an ambulatory patient an energy storage module configured to store an electrical charge a discharge circuit coupled to the energy storage module; electrodes configured to sense an Electrocardiogram signal of the patient; a processor configured to: set a noise-detected flag responsive to the sensed ECG signal meeting a High-Amplitude (H-A) noise criterion, and unset the noise-detected flag responsive to the sensed ECG signal meeting a High-Amplitude (H-A) quiet criterion, wherein the H-A noise criterion is met when a noise fraction of a group of ECG portions in a sensed ECG signal comprising a number of potential R peaks exceeding a threshold amplitude exceeds a threshold noise fraction and the H-A quiet criterion is met responsive to the H-A noise criterion no longer being met, determine, from the sensed ECG signal, whether or not a shock criterion is met, and control, responsive to the shock criterion being met and the noise-detected flag being unset, the discharge circuit to discharge the stored electrical charge through the patient while the support structure is worn by the patient so as to deliver a shock to the patient, but the discharge circuit is controlled to not thus discharge when the noise-detected flag is set even if it is thus determined that the shock criterion is met. a support structure configured to be worn by an ambulatory patient an energy storage module configured to store an electrical charge a discharge circuit coupled to the energy storage module; electrodes configured to sense an Electrocardiogram signal of the patient; a processor configured to: set a noise-detected flag responsive to the sensed ECG signal meeting a High-Amplitude (H-A) noise criterion, and unset the noise-detected flag responsive to the sensed ECG signal meeting a High-Amplitude (H-A) quiet criterion, wherein the H-A noise criterion is met when a noise fraction of a group of ECG portions in a sensed ECG signal comprising a number of potential R peaks exceeding a threshold amplitude exceeds a threshold noise fraction and the H-A quiet criterion is met responsive to the H-A noise criterion no longer being met, determine, from the sensed ECG signal, whether or not a shock criterion is met, and control, responsive to the shock criterion being met and the noise-detected flag being unset, the discharge circuit to discharge the stored electrical charge through the patient while the support structure is worn by the patient so as to deliver a shock to the patient, but the discharge circuit is controlled to not thus discharge when the noise-detected flag is set even if it is thus determined that the shock criterion is met. set a noise-detected flag responsive to the sensed ECG signal meeting a High-Amplitude (H-A) noise criterion, and unset the noise-detected flag responsive to the sensed ECG signal meeting a High-Amplitude (H-A) quiet criterion, wherein the H-A noise criterion is met when a noise fraction of a group of ECG portions in a sensed ECG signal comprising a number of potential R peaks exceeding a threshold amplitude exceeds a threshold noise fraction and the H-A quiet criterion is met responsive to the H-A noise criterion no longer being met, determine, from the sensed ECG signal, whether or not a shock criterion is met, and control, responsive to the shock criterion being met and the noise-detected flag being unset, the discharge circuit to discharge the stored electrical charge through the patient while the support structure is worn by the patient so as to deliver a shock to the patient, but the discharge circuit is controlled to not thus discharge when the noise-detected flag is set even if it is thus determined that the shock criterion is met.