The QRAE II Pump or Diffusion
http://www.raesystems.com/products/qrae-ii-pump is a full-featured, compact, one- to four-sensor gas detector for oxygen, combustibles, hydrogen sulfide, carbon monoxide or sulfur dioxide. Key features include an easy-to-change battery pack, a water-resistant case and a new state-of-the-art ROHS compliant O2 sensor. More information at www.raeystems.com