The Triplett GSM250 Desktop Indoor Air Quality CO2 Meter can be used to monitor air quality in office buildings, schools, exhibition halls, shopping malls, meeting rooms, fitness centers, restaurants and other public places. The Triplett GSM250 simultaneously displays CO2, Temperature and Relative Humidity. It can be used on the desktop or wall mounted and has a display with a light bar for easy reading from long distances. A 3-color light bar (green / yellow / red) changes color with CO2 concentration. The Triplett GSM250 has touch panel programming and a user-adjustable CO2 level alarm with disable. NDIR (non-dispersive infrared) waveguide technology use automatic baseline calibration (with disable) for long term drift compensation or 400ppm manual calibration. The meter does not use batteries and requires power from a USB source: PC, Power bank, 5VDC wall adapter (not included). 1 year warranty.