1Maximum/minimum hold feature for measuring absolute high/low peaks and hold datas. 2A great necessity tool to test H2S gas, perfect for using in biological medicine, fire detection and so on. 3When the concentration of H2S in the air exceeds the standard, sound and light alarm will be issued immediately, and the concentration value of carbon monoxide will be displayed. 4The product is ergonomically designed for easy handling and operation, perfect for household and working testing. 5In order to ensure longer battery life, you can set the timing switch machine, saving the time of manual switch machine. Features: 1. Maximum/minimum hold feature for measuring absolute high/low peaks and hold datas. 2. A great necessity tool to test H2S gas, perfect for using in biological medicine, fire detection and so on. 3. When the concentration of H2S in the air exceeds the standard, sound and light alarm will be issued immediately, and the concentration value of carbon monoxide will be displayed. 4. The product is ergonomically designed for easy handling and operation, perfect for household and working testing. 5. In order to ensure longer battery life, you can set the timing switch machine, saving the time of manual switch machine. Specification: Item Type: H2S Detector Material: ABS Measurement Range: 0-100PPM: 0-0.01VOL%; 0-152Mg /m; 0-0.23LEL% Maximum Overload: 500PPM Response Time: <30 seconds Sensor Type: Electromagnetic H2S sensor Ambient Humidity: 15-90% RH Battery: 3 x 1.5V AA Battery (Not Included) Package List: 1 x H2S Detector 1 x Instruction 1 x Black Box