Carbon monoxide is an invisible, unscented and at high levels can be a deadly gas. Lower concentrations of carbon monoxide can cause headaches, lightheadedness and fatigue. Winter months may pose health and safety risks with heating systems. Poorly maintained chimneys and flues may release carbon monoxide and other harmful gases into the air. If your home is heated by gas, coal, or oil you are required to install a carbon monoxide detector according to Chicago Ordinance.