Crash test dummy kinematics is commonly obtained from high-speed video recordings or other optical methods which are processed to provide displacements as functions of time. This study presents an open-source software that can provide motion data from sensors in the dummy. Sensors needed for this analysis are a combination of gyros and accelerometers. The evaluation was done using the crash tests dummies SET v0.2 50F and 50M, developed for low severity rear impacts and equipped with gyros at four locations, one inside the head and at three locations along the spine. The tests were done in two different seats in 16 km/h rear impact sled tests. The analysis showed good agreement between high-speed film analysis using Tema and the motion from the sensors. The motion in focus in this study is the loading to the neck caused by the head and the torso (the first thoracis vertebrae). Motion data from sensors could provide a more direct approach to identify which seats provide the lowest load on the neck, in testing, due to relative motion between the head and the torso, without requiring time-consuming camera setup and manual analysis. Furthermore, sensors have the potential to provide higher resolution results and measurements of movements that are difficult to capture through optical methods.