Biosystem® PhD5 Confined Space Gas Detectors Monitor up to five atomspheric hazards simultaneously; oxygen, combustible gas, and up to three channels of toxic gas detection. Innovative Duo-Tox two-channel sensor measures both CO and H2S when both are present without cross interference. All procedures necessary for day-to-day operation, including automatic calibration, are controlled through the single On/Off "Mode" button. Rugged, metal-plated case stands up to the most demanding environments. PhD5 Gas Detectors come with NiCad battery.