A rugged, compact, easy-to-use instrument for O2, LEL, CO and H2S measurement. All four sensors, including oxygen, are warranted for three full years after purchase, significantly reducing the cost of ownership. Interchangeable alkaline and rechargeable battery packs provide up to 25 hours of operation. The top-mounted display changes color just like a traffic signal from green to amber to red as a function of the severity of the alarm condition. The durable, highly water resistant housing includes a built in rubberized boot, protecting the instrument from damage due to bumps or tough environmental conditions. The optional motorized pump has its own power supply, and uses the same interchangeable battery packs as the G450. Optional docking station provides automatic "bump" test, calibration, charging and record keeping. MSHA approved G450 available.