RKI Single Gas Monitor HS-04The 04 Series single gas monitor is designed to operate for many years with field replaceable sensors and filters. The 04 Series can be operated continuously for up to 9,000 hours on (2) AAA size alkaline batteries (depending on model). The 04 Series has 3 preset alarms that are user adjustable. Each version is also equipped with visual, audible, and vibration alarms as standard. The replacement sensors are inexpensive, easily field replaceable, and