There are several types of airbag sensor available today. Each type of sensor has unique response characteristics to impact. Mathematical models for five types of sensor, three mechanical, two electronic, have been developed, in order to clarify the difference of the characteristics. First, three mechanical sensors are examined at marginal and high speed crash. And it was found that two(spring-mass sensor and rotary sensor) of these three sensors have almost same characteristics, and the other (air-damped sensor) is unique as it is more sensitive to velocity change, and its response is influenced by cross-axis vibration too, at low speed crash. Second, five sensors including two electronic ones are compared as a single point sensor(a sensing system detecting a crash at a single location of the vehicle). From the comparative study, an electronic sensor which is sensitive both velocity change and vibration is derived to be most desirable from a viewpoint of crash detection.