Hand injuries from repetitive high-strain and physical overload can hamper or even end a musician's career. To help musicians develop safer playing habits, we developed a multiplecontact force-sensing array that can substitute as a guitar fretboard. The system consists of 72 individual force sensing modules, each containing a flexure and a photointerrupter that measures the corresponding deflection when forces are applied. The system is capable of measuring forces between 0-25 N applied anywhere within the first 12 frets at a rate of 20 Hz with an average accuracy of 0.4 N and a resolution of 0.1 N. Accompanied with a GUI, the resulting prototype was received positively as a useful tool for learning and injury prevention by novice and expert musicians.