Carbon monoxide Carbon monoxide is a byproduct of the combustion of natural gas, oil, wood, or any carbon-based fuel. It is a clear, odorless, and tasteless gas, and can cause death if gone undetected. Extended exposure to low levels (sometimes not detected by inexpensive carbon monoxide detectors) can cause long-term health problems. Carbon monoxide alarms with a minimum sensitivity of 30 parts per million (ppm) (the greater the sensitivity, the better) and with no time delay should be installed at locations where oil or natural gas appliances or fireplaces are used. We recommend adding carbon monoxide alarms to bedrooms and any other areas where people are likely to fall asleep (such as a family room with a cozy fireplace, television, and stereo). We also recommend installing at least two carbon monoxide alarms in all residences to provide backup protection if a dead battery is present in one or if an alarm is defective or fails. There are many different types of carbon monoxide alarms available, some that can simply be plugged into an electric outlet. Testing, inspection, analysis, or opinion of function of carbon monoxide alarms is not within the scope of the home inspection. Information concerning the location of any carbon monoxide alarms is presented as a courtesy to Client. The built-in test button, when present, only verifies proper battery and alarm function; it does not test sensing capabilities. We do not specifically look for carbon monoxide alarms,but if they are noticed, their location is noted. Some carbon monoxide alarms might have been outlet plug-in units and might not have been visible due to furnishings and storage or might have been taken by the occupants during move-out. Recommend testing carbon monoxide alarms at move-in, installing fresh batteries, and testing all alarms weekly. If carbon monoxide alarms are not present in the residence, recommend having at least two installed.