Spectrum sensing at low signal-to-noise ratio regimes is a challenging area that has recently attracted much interest from the research community. In this letter, two novel detectors for weak signals are presented, the phase-rotated spectral correlation detector and the complex-decomposition-based PSCD, by means of exploiting the linear relationship between samples from two sampling channels. False alarm and detection probabilities of the proposed detectors are found based on statistical theory. Detection performance metrics of the proposed detectors in terms of the deflection coefficient and receiver operating characteristic are evaluated in additive white Gaussian noise channels. Analytical and simulated results indicate that the proposed detectors are blind detection techniques and outperform the energy detector and single-cycle cyclostationary detector.