A variety of experiments with smartphones and tablet PCs allow a precise analysis of acoustic phenomena. For example, we recently described an experiment in which a noise signal simultaneously triggered harmonic acoustic resonances in the air column of a tube open at both ends and a tube closed at one end. The measured resonant frequencies were used to determine the speed of sound in air with an error less than 4%. The present article describes experiments for harmonic resonances in another type of one-dimensional wave carrier, viz. clamped metal rods. Resonances are generated by hitting one end face of the rod; the resonant frequencies can then be measured by an app on a smartphone or tablet PC. The experiments can be used to explore how the excitement of particular resonant frequencies depend on boundary conditions like the length of the rod, the number and specific positions of fixed points of the rod, and the rod's material. In addition the rod's longitudinal (the so-called extensional) speed of sound can be determined.