BW Technologies MCXL-XWHM-Y-NA GasAlertMicroClip XL 4 Gas Detector, CO, H2S, LEL and O2, Yellow Four-gas detector for surveying levels of H2S, oxygen (O2), carbon monoxide (CO), and combustibles in natural and industrial environments, and in other personal safety, training, research Easy and comfortable to wear; thin and lightweight, ambient air monitoring applications Easy operation and straightforward training with one-button simplicity Easy visual compliance with flashing, green IntelliFlash LCD screen shows up to four ambient gas concentrations, battery level, alarm condition, and the status of calibration, bump, and sensor self-tests