T-GAS-MCD -- (Multi-Channel Multi-Zone Toxic Gas Monitor) 4-20 mA Controller -- (for Measurement, Display and Alarm processing of 4-20 mA sensors) 4-20 mA Remote Sensors-- (to Provide 4-20 mA analog signal to MCD monitors or your system) Built In Options-- (for T-GAS MCD Monitors) Accessories-- (for T-GAs MCD Monitors)