This paper analyses the Sum-of-Squares (SoS) detector which is designed to reveal the presence of a spoofing attack. The SoS decision statistic is computed using carrier phase measurements from two spatially separated GNSS receivers and assumes a simple form which make it suitable for real-time applications. The detector is theoretically characterized and its effectiveness is shown using simulations and experiments involving real GPS data.JRC.E.2-Technology Innovation in Securit