Crowcon T4 [T4-HOCA-H2] 4-Gas Portable Multigas Detector, H2S, CO2, CO-H2 and CH4 T4-HOCA-H2 4 Gas Sensor, Detects Hydrogen Sulfide (H2S), Oxygen (O2), Carbon Monoxide (CO - H2 Resistant) and Methane (CH4). T4 integrates innovative safety features and an intuitive, rugged design to provide advanced protection for those working in harsh environments. This portable multi-gas detector, which is exceptionally easy to use and service, protects against the four most prevalent gas hazards: carbon monoxide (CO), hydrogen sulphide (H2S), flammable gases and oxygen (O2) depletion.