Single Gas MonitorsSingle Gas MonitorsSingle Gas MonitorsSingle Gas MonitorsSingle Gas Monitors

Single Gas Monitors

  • RKI - CO-04, HS-04, OX-04, CX-04

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04 Series – Single Gas Monitors

The 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 are interchangeable with other popular RKI instruments like the GX-3R, GX-3R Pro, and GasWatch 3. Sensors have a life expectancy of over 3 years and are backed by a 3 year warranty.*

Each 04 Series monitor is impact, dust, and water resistant with an IP-67 ingress protection rating. 04 Series instruments are safe for use in hazardous locations, classified as intrinsically safe ATEX/IECEx and by QPS to U.S. and Canadian standards for Class I, Division 1, Groups A, B, C, and D atmospheres.

* 3 year warranty on material and workmanship including sensors (1 year warranty for Ammonia and Chlorine sensors)


  • Continuously operate for over one year (H2S & CO)
  • Toxic gases include: NH3, Cl2, HCN, NO2, PH3 & SO2
  • CO with H2 elimination
  • CO & O2 Dual Sensor
  • Field serviceable
  • Pocket size 2.1”(W) x 2.6”(H) x 0.9”(D),2.8 ounces
  • Impact, dust, and water resistant (IP-67)
  • Replaceable rubber boot
  • Alligator clip with 360° rotation
  • Audible / visual / vibration alarms
  • Automatic backlight
  • Intrinsically safe, ATEX and C / US approvals
  • 3 Year warranty*


  • Hazardous material
  • Mining
  • Refineries / petrochemical
  • Water / wastewater treatment
  • Pharmaceuticals
  • Utilities
  • Chemical plants
  • Fire services

Common Specifications

Sample MethodDiffusion
Response TimeT90 in 30 seconds
Alarm TypesGas alarm Trouble alarm
1st, 2nd, and 3rd (user adjustable),OVER alarm, STEL, and TWASensor connection, low battery, circuit failure,and calibration range error
Alarm MethodsGas AlarmTrouble AlarmSTEL / TWA
Flashing LED’s, intermittent buzzer, flashing gas value, and vibrationFlashing LED’s, intermittent buzzer, and display of error messageFlashing LED’s, intermittent buzzer, flashing gas value, and vibration
Datalogging10 sec. intervals = 10 hrs. 5 min. intervals = 300hrs, 10 min. intervals = 600 hours
Instrument records alarms, alarm trends, gas readings, calibration & bump test history, instrument settings
Battery OptionsAlkaline dry cell (2-AAA size)
DisplayDigital LCD, gas name & concentration, auto backlighting during alarm, operation icon, battery icon
Operating Temp. & Humidity-4°F to 122°F (-20°C ~ +50℃),0- 90% RH non condensing
Dimensions2.1” W x 2.64” H x 0.94” D (54 x 67 x 24 mm)
2.8 ounce (80g)
EnclosureDust and water resistant with IP-67 rating
Safety RatingATEX/IECEx approved. QPS classified, “C / US”, as intrinsically safe, Class I, Division 1, Groups A, B, C, D
Standard Accessories• Rubber boot • Datalogging software • Alligator clip • Alkaline batteries
Optional Accessories
  • Calibration cap
  • Wrist strap
  • Calibration kit
  • Belt clip
  • Datalogging download cable
Special FunctionsManual backlight for LCD (automatically lit during alarm),Peak hold, STEL & TWA
Warranty3 year warranty (1 year for Ammonia and Chlorine)

Gases & Detectable Ranges

GasModelsDetection Range (Increments)Accuracy StatementAlarm Set PointsContinuous Operation
Hydrogen Sulfide (H2S)HS-040 – 200.0 ppm (0.1 ppm)± 5% of reading or ± 2 ppm H2SA1: 5 ppm9,000 hours
A2: 30.0 ppm
A3: 100.0 ppm
TWA 1.0 ppm
STEL 5.0 ppm
Carbon Monoxide (CO)CO-040 – 2000 ppm (1 ppm)± 5% of reading or ± 5 ppm COA1: 25 ppm9,000 hours
A2: 50 ppm
A3: 1200 ppm
CO (-H2)CO-04C± 5% of reading or ± 2 ppm COA3: 1200 ppm6,200 hours
TWA 25 ppm
STEL 200 ppm
Oxygen (O2)OX-040 – 40% Vol. (0.1%)± 0.5% O2A1: 19.5 Vol.3,000 hours
A2: 18.0 Vol.
A3: 23.5 Vol.
CO / O2
Dual Sensor
0 - 2000 ppm
(1 ppm)
± 5% of reading or ± 2 ppm H2SA1: 25 ppm4,600 hours
A2: 50 ppm
A3: 1200 ppm
TWA 25 ppm
STEL 200 ppm
0 - 40% Vol.
± 0.5% O2A1: 19.5 Vol.
A2: 18.0 Vol.
A3: 23.5 Vol.