This paper gives the design & development of a carbon monoxide detector. Living in cities is convenient in many ways such as high-quality public services such as healthcare and education. However, for all the advantages offered by city living, it has not come without its own costs. Pollutant levels such as Carbon Monoxide in urban environments are sometimes unacceptably high. In many heavily urbanized areas, particularly in the developing world such as China, India and Brazil, carbon monoxide detectors often register levels many times higher than accepted ‘safe’ levels. Unfortunately, this is by no means a problem exclusive to the developing world, with many major cities as far afield as Singapore, Seoul, London, New York and Los Angeles also regularly experiencing unsafe Carbon Monoxide levels. (CO) is a colourless, odourless gas which at high levels can cause serious illness and death. CO alarms are widely available and should be considered a backup to BUT NOT A REPLACEMENT for proper installation, use, and maintenance of fuel-burning appliances. CO alarms are designed to warn you of any unusual build-up of CO in your home. These higher levels of CO may occur from improperly maintained, installed or used fuel-burning appliances, back drafting appliances or fireplaces, or idling cars in garages. If a CO alarm is to be installed.