This ozone detector is the one you want to use to determine if the ozone (O3) gas has reached high enough levels within a treatment area to be effective. It measures ozone gas between 0-20 ppm (parts per million). For example, according to a report from the US Army, to kill virus with ozone you should reach at least 2.5 ppm for 30 minutes. This detector will provide an accurate reading of high levels of ozone. For specialized applications only - this detector is not required for personal use. This is not the detector to use to test whether the ozone has reached low enough levels to be safe for occupants. For safety monitoring, find the "ozone sensor" in our shop.