Surface electromyography (sEMG) is a noninvasive technique widely used to control myoelectric prostheses and other human-machine interfaces. However, the high cost of commercial systems limits accessibility in academic and research environments, especially in developing countries. This study presents a validation protocol for a low-cost eight-electrode sEMG wristband prototype based on IEC 60601 and ANSI/AAMI EC13 standards. The protocol includes electrical safety tests, such as leakage current measurement, insulation evaluation, and continuity verification between electrodes and circuits. Functional performance was evaluated by comparing signals acquired with the prototype against those obtained from a commercial reference device (PortiLab2) using Pearson correlation, Bland-Altman analysis, and mean squared error. Additional tests included signal stability during rest and contraction, UART and Bluetooth communication, frequency response, mechanical characterization of the casing, and user comfort assessment. Results showed leakage currents between 11.4 uA and 13.5 uA, adequate insulation, stable signal acquisition, and high correlation with the reference system (r > 0.85). Reliable wireless transmission without packet loss was also observed. Limitations included power supply constraints during wireless testing and discrepancies in the frequency response at high-gain stages compared with simulations. Mechanical tests showed elastic behavior of the casing under loads up to 98 N. The proposed protocol provides a practical and reproducible framework for the technical and functional validation of low-cost sEMG systems for research and educational applications.