This publication reports on the design, fabrication, and testing of an improved methane monitor system for compliance with 30 cfr 75.313. The system will initiate automatic shutdown of mining machinery when excessive concentrations of methane are encountered. The prime considerations in the design were small size, improved accuracy and reliability, fast response, and a transient-resistant power supply capable of reliable operation from any mine power source. The power supply contains an internal battery that provides operating power to the detection system prior to mining machine start-up or after machine shutdown. This report documents the development program from conception through in-mine testing.