The invention discloses a signal detection apparatus and method thereof for detecting whether an input signal of a set of serial ATA signals is an out of band (OOB) signal. The signal detection apparatus includes a calibrated clock generation device, a signal processor, and a logic determination device. The calibrated clock generation device generates a sampling clock signal according to a predetermined clock signal. The signal processor generates a plurality of detection results based on the sampling clock signal and the input signal. The logic determination device receives the plural of detection results and determines whether the input signal is the OOB signal.