Single-gas Model pm-90 monitors O2, CO, H2S, or NO2, averaging over 5,000 hr operation from standard 9 V battery; 10,000 hr from 9 V lithium battery. Sealed nickel alloy-plated polycarbonate case protects against RFI, EMI, water, and dust. Large backlit LCD eases setup and calibration. Instrument can interchange smart sensors while retaining calibration information. It includes visual (LED), vibrating, and loud pulsating alarm.