Polarization changes inside a single-mode fiber due to birefringence are studied in this paper. We demonstrate a measurement system for the detection of fast and slow polarization transients in a single-mode optical fiber route. The output signals from a polarimeter based on tilted fiber gratings and a polarimeter based on a polarizing beam splitter and a balanced detector (PBS polarimeter) are processed. The processed data reveal that the detected signal depends on the vibration along the fiber route caused by trains and the temperature instability around the fiber. The proposed system is sufficient for detecting polarization transients and can be used for the detection of suspicious events that would lead to a disruption of the optical path.