a shock sensor has a housing with two portions . a first portion resiliently engages a reed switch which has staple formed leads . a second portion extends adjacent one of the reed switch leads and has modular components which permit consistent shock - sensing results to be obtained from reed switches of varying sensitivity by selection of appropriate components . the second portion is a closed - ended hollow tube in which a bobbin with a centrally located guide bar is inserted . a first disk extends outwardly from the guide bar . a self - test coil is positioned on the bar between the first disk and a second disk . a biasing spring extends between the closed end of the tube and the magnet , which is mounted on the bar . the magnet is abutted against a second disk which extends from the bar . the second disk positions the actuation magnet with respect to the reed switch when it is in its non - actuated position . by substituting different bobbin and the actuation springs , shock sensors are easily created which achieve identical functions with reed switches of varying amp turn requirements for actuation .