Matt Mueller, creator of soundscience.education, was inspired by David Wells, the director of maker programming at the New York Hall of Science, and his methodology for running science of sound workshops. Piezo vibration sensors work well to demonstrate the way that vibrations travel through different materials of different dimensions and start a discussion about why instruments are made how they are. The tricky part is that the electrical signal induced by the vibrations of the piezo crystal need to be amplified in order to be audible through a headphone or speaker. Matt created a design that contains the piezo sensor and a battery connected to a custom circuit to amplify the signal inside, and a headphone jack with a volume knob on the outside. Placing these components in a 3D printed case with a rounded top, you can then touch it against any surface and hear what vibrations sound like through that material. Check out the instructable below to learn more or make your own!