Abstract: A crash sensor for a passive motor vehicle occupant restraint system, such as an inflatable air bag or seat belt tensioner. The crash sensor comprises a tubular passageway having a central, longitudinal axis; a sensing mass arranged to move within the passageway in the direction of the longitudinal axis between a first location and a second location; a device for biasing the sensing mass toward the first location in the passageway; and a device for closing an electrical circuit when the sensing mass moves to the second location in the passageway.The invention provides methods for reducing the motion of the sensing mass and the tubular passageway in a direction perpendicular to the longitude, and/or methods for reducing the angular momentum of the sensing mass, during motion of the sensing mass in the longitudinal direction.