Visibility of invisible CO2 concentrations in color and numerical value This air quality monitor allows you to see when ventilation is at a glance. Displays the concentration of CO2 from 400ppm to 5,000ppm If the above 1000 ppm is possible, you can also hear a warning sound (can be switched on and off). In addition, it can also display space temperature and humidity. It is also a great device for restaurants, offices, and more. It can be charged by USB (micro-USB), and it is equipped with an internal battery, so it can be used anywhere.