This paper presents a novel real-time monitor for power systems. This monitor is designed to track the waveforms of signals of interest during power system operations, including the transients caused by load changes or faults. State estimation techniques are used to detect sampling errors in order to best track the trajectory of the original signal waveforms. Our previously proposed algorithms are then used to perform an observability analysis for a given set of measurements. A new measurement equation is introduced to detect bad data processing. Numerical results illustrate the effectiveness of the proposed tracking monitor.