Methods, noise detection devices, and differential voltage measuring systems are provided for detecting noise signals for the purpose of measuring cardiac movements in a patient. In the method, contact is made with the patient by at least two measuring electrodes having at least one associated measuring channel. Furthermore, a heartbeat measurement is performed. During the heartbeat measurement, signals from the patient are detected over the at least one measuring channel. Then, a check is made of whether the detected signals have been caused by noise by comparing the detected signals with at least one heartbeat type that was identified in the course of the learning procedure.