CGA 501 GAS-SENTRYT MONITOR Bascom-Turner Instruments: Simultaneously monitors ambient air for combustible gas, carbon monoxide, hydrogen sulfide, and oxygen. Internal pump allows confined space air sampling with long hose and probe prior to entry. Breath zone probe (clipped to collar) samples breath zone air. LED display flashing and acoustic alarm sounds when alarm levels are exceeded. Forty hours of operation on four AA batteries. Automatically calibrates in less than 60 seconds when sampling calibration gas. (800) 225-3298.