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 .