Seat-occupancy-detection-sensor-element featuring double-body/compression/spring (DBCS) in a recess of a base-member (BM); and slidable-member (SM) having a force-application-side (FAS) and inside facing the BM; measuring-coil (MC) arranged in the recess and surrounded by the DBCS and having wound-coil-wire (WCW); and current-generating/measuring/evaluating-unit (CGMEU) connected to the WCW; the DBCW abutting the BM on one side and being fixed to the SM on the side of the SM compressed by a force on the FAS, from a spring length either uncompressed or compressed by a predetermined extent; spring wire ends connected and electrically forming a spring-coil (SC); MC and SC coils constituting an inductively-coupled coil assembly (ICCA); and the CGMEU applying AC to the MC inducing AC in the DBCS, measuring voltage on the MC proportional to the ICCA's impedance, and ascertaining force on the SM's FAS.