The S102 is an inertial seismometer that measures ground motion with respect to an elastically suspended mass. Precision agate bearings and a hardened knife-edge pivot ensure long life. A linear, low noise RF displacement detector is used to sense the position of the reference mass with respect to the instrument housing. The reference mass is controlled in an electronic feedback loop by means of a moving magnet transducer. This feedback loop provides near critical damping of the system, resulting in an extended frequency response, and eliminating thermal noise, hysteresis and stiction normally associated with conventional mechanical systems. The transfer function of the S102 has nearly constant sensitivity to the vertical component of ground motion, and is similar to that of the moving coil sensors used in the World-Wide Standard Seismic Network.