Carbon monoxide (CO) is a toxic gas usually formed during the incomplete combustion of carbon-based fuels. Poisoning by CO can be fatal or lead to long-term debilitating cardiovascular, respiratory and neuropsychological conditions. Despite the reinforcement of government policies on CO poisoning over the past decade, emergency practitioners should become more aware of CO toxicity to reduce mortality and morbidity, and an unnecessary financial burden on health services. This article alerts emergency nurses to the signs and symptoms of CO poisoning and discusses the use of non-invasive CO-monitoring devices to confirm levels of CO in patients' blood and exhaled air. It also considers the case for early CO monitoring in emergency care settings.