Feature: can detect hydrogen sulfide,Carbon monoxide,oxygen and methane in the same time. 1. Choose randomly from the following 4 gases CO,H2S,02 and CH4 (combustible gas) 2. Big liquid crystal display can indicate the data, character and the symbol at the same time 3. Unique backlight function guarantees easy reading even in dark working environment 4. Alarming function can be adjusted. It has calender and clock function as well 5. Alarm is available for gas in high concertration, low concentration, STEL TWA low electric quantity alarm and low current alarm. 6. Unique function of large capacity for data memorizing and downloading 7. Automatic protection function for outrange of combustible gases 8. Unique lithium ion battery and can work for 18 hours Detecting range CO: (0-999)ppm,resolution: 1ppm H2S: (0-100)ppm,resolution: 1ppm 02: (0-30%)VOL,resolution: 0.1% CH4 (0-5.0%)CH4,resolution: 0.01%