We present the FingerSynth, a wearable musical instrument made up of a bracelet and set of rings that enable its player to produce sound by touching nearly any surface in their environment. Each ring contains a small, independently controlled exciter transducer commonly used for auditory bone conduction. The rings sound loudly when they touch a hard object, and are practically silent otherwise. When a wearer touches their own (or someone else's) head, the contacted person hears the sound through bone conduction, inaudible to others. The bracelet contains a microcontroller, a set of FET transistors, an accelerometer, and a battery. The microcontroller generates a separate audio signal for each ring, switched through the FETs, and can take user input through the accelerometer in the form of taps, flicks, and other gestures. The player controls the envelope and timbre of the sound by varying the physical pressure and the angle of their finger on the surface, or by touching differently resonant surfaces. Because its sound is shaped by direct, physical contact with objects and people, the FingerSynth encourages players to experiment with the materials around them and with one another, making music with everything they touch.