Easily monitor indoor air quality with this reliable and accurate TVOC and CO2 monitor. The Taylor Digital Air Quality Monitor continuously measures TVOC (Total Volatile Organic Compounds) and CO2 (Carbon Dioxide). The unit can be programmed to have an audible alert when CO2 levels rise to the "POOR" classification or a set level based on personal sensitivities. The trend bars will update every hour and show a rising, neutral, or lower trend arrow. This device is designed for indoor use only. For optimal sensor readings, keep your device away from direct sunlight and in less than 500 square feet of open space. For best results, keep plugged in with the USB cord.