A signal detector and a signal detection method adapted for detecting a voltage signal are provided. According to a digital signal converted from a low voltage full wave or half wave signal and/or a mains AC signal inputted thereto, the signal detector and the signal detection method are capable of detecting a voltage level, and/or a frequency, and/or a zero point, and/or a phase of the low voltage full wave or half wave signal and/or the mains AC signal inputted thereto, and determining whether the detected factor is abnormal, and is further capable of outputting an interrupt signal for subsequent processing.