A model scanning probe microscope, designed using similar principles of operation to research instruments, is described. Proximity sensing is done using a capacitance probe, and a mechanical linkage is used to scan this probe across surfaces. The signal is transduced as an audio tone using a heterodyne detection circuit analogous to that used in the theremin (one of the first electronic musical instruments, invented in the early 20th century). The instrument is useful for demonstrations and hands-on activities that introduce fundamentals of scanning probe microscopy and, by extension, nanoscience and nanotechnology. The details of instrument construction are provided, along with instructions for assembly and troubleshooting.