This paper discusses dual-stage detection scheme of a Single-carrier Frequency Division Multiple Access (SC-FDMA) signal. The proposed scheme is composed of the coarse detection stage and the refined detection stage. Different from conventional double-step detection schemes, we focus on the integration of two detection stages. The threshold factor and the probability of uncertainty are first proposed and defined to combine such two stages. The relation between the threshold factor and the probability of uncertainty is also shown by theoretical analysis and computer simulations. A tradeoff between the detection performance and the computational complexity can be achieved by setting the probability of uncertainty ahead according to the detection environment or the type of the primary signal. The proposed scheme is suitable for the detection in the detect and avoid (DAA) mechanism of Ultra-Wideband (UWB) systems. Simulation results indicate that the dual-stage detection scheme can achieve the target detection performance by setting the probability of uncertainty.