This invention includes crash sensors designed to be used for frontal impact sensing and the strategies of using these sensors. It is analyzed and shown that velocity sensing or damped sernsors are desirable for frontal impact passenger compartment sensing. inertially damped sensors, with a damping force proportional to the square of velocity, is preferred for some applications. In other cases a viscous damped sensor is appropriate and in a few cases an undamped spring mass sensor will suffice. Such sensors can be made of plastic and in the shape of short housings. A preferred embodiment of this invention utilizes a swinging mass hinged to a housing as the sensing mass. Different geometries of the mass and the housing are disclosed and used to improve the performance of such sensors. These flapper mass sensors are useful for sensing frontal impacts in the passenger compartment both as primary sensors and as single or dual contact arming sensors. A method of manufacturing these sensors is also disclosed, in which the contacts are treated to become adhesive to plastic and then molded with the remaining plastic parts of the sensors. The plastic parts are then welded to form a hermetically-sealed interior of the sensor.