Recent trends in earthquake monitoring and prediction have focused on the monitoring of seismic frequencies that are very close to the natural frequencies of buildings and other structures, such as bridges. This paper introduces a new type of seismic sensor that is highly sensitive to vibrations at one specific frequency. The sensor inherently rejects vibrations at all other frequencies. The sensor's characteristic frequency must be tuned to match the natural frequency of the building or structure that is being monitored. The sensor is based on the fundamental principle of coupling an oscillating mass-spring system with an electromagnetic transducer consisting of a space charge and a toroidal coil. Analysis and experimental results show that the frequency selectivity of such a vibration sensing mechanism is substantially high.