This paper presents a study of air bag sensor performance in low threshold speed tests where air bag deployment is desired. It presents the effects of the bumper energy absorbing system and the sensor mounting bracket on sensor performance. Vehicle crash deceleration pulses were analyzed for their filtered characteristics and then used as inputs in two mathematical models. One model simulates the dynamic response of a sensor mounting bracket subjected to rotation of the bracket support structure;​ the other, the dynamics of an air bag ball-in-tube sensor during a crash. The bumper system plays an important role in providing an early deceleration signal needed for air bag sensor activation at low threshold speeds. Sensor bracket support rotation can have an appreciable effect on the deceleration level detected by the sensor. For the type of sensor bracket considered in this study, the vibration of the bracket itself did not significantly change the deceleration level detected by the sensor. Graphs are presented showing the influence of the bumper system and the sensor mounting bracket design on sensor dynamic performance. An animated technique is used to visually present the interaction between the responses of structural components and activation of the air bag sensor. Performance of the air bag sensor under these various test conditions is discussed.