“…If this hypothesis is not satisfied, the accuracy and reliability of the classical fault detection techniques, and therefore of the whole system where the devices are inserted, are compromised (Vioarsson et al, 2000); (Bruce et al, 2000). In this context, this book chapter collects and summarizes the last years proposals about the use of Generalized Likelihood Ratio test (GLRT) as a fault detection technique, complementary to the classical ones, for revealing faults from frequency data (E. Nunzi et al, 2007); (E. Nunzi et al, 2007); ; ; (E. Nunzi & D. D'Ippolito, 2009); ). In particular, the GLRT (S. M. , following the Neyman-Pearson (NP) approach is presented and its effectiveness is demonstrated when clock frequency data are subjected to jumps in the mean and/or in the dynamic range.…”