Crash sensors for the air bag system may be broadly divided into mechanical and electronic devices. The mechanical sensor is based on the idea to balance an external force working on the mass against a bias force which is basically proportional to the displacement of the mass. The characteristics of such bias force can be brought very close to an optimum state by properly designing the sensor system. Studies are also well under way on the relationship between damping and mass displacement to make it satisfy the requirements for the air bag system. The electronic sensor features the capability of changing its characteristics through a computer program.The positioning of sensors in the vehicle should be decided on taking their characteristics into consideration. In addition to the crash tests required under the applicable laws and regulations, we have elected to conduct a series of other tests simulating a variety of crash modes that may occur on the road. This report discusses a proposed idea for such real-world tests.Some examples of sensors, connectors and the ways they are linked together are also given in the report to show major considerations in making the air bag system reliable.