Models OX-01, CO-01, HS-01, GP-01 Individuals need personal protection in hazardous areas at all times without adding extra bulky equipment, and the 01 Series can provide that kind of protection at an affordable price. The GP-01, OX-01, CO-01, HS-01 and HS-01S models are personal single gas monitors designed for personal protection from combustible hydrocarbons, oxygen deficiency, hydrogen sulfide, or carbon monoxide. Each model is controlled by a microprocessor for reliability and advanced capabilities. Each model can be operated continuously for at least 3,000 hours on (2) AAA size alkaline batteries except the GP-01, which operates for 16 hours. The 01 models have 2 preset alarms that are user adjustable and each version is also equipped with visual, audible, and vibration alarms as standard. The replacement sensors are inexpensive, easily field replaceable, have a life expectancy of 2 years, and are interchangeable with other RKI monitors such as the GX-2001, GX-2003, and GasWatch 2 models.