Carbon monoxide gas is a major source of environmental pollutant that emanates from fuel combustion with limited oxygen. The gas is lighter than the air and could be poisonous and dangerous if inhaled in high quantity by human beings. To prevent or reduce this poisoning and its effects, it is imperative to design and construct a detector that can assess the carbon monoxide levels in an environment and provide the concentrations level. The design involves assembling MQ-7 sensor and Atmega 328 microcontroller as the processor. Analogue input from carbon monoxide sources is converted to digital output and the result is displayed using Liquid Crystal Display (LCD). The output voltage of carbon monoxide emitted from vehicles, petrol and diesel generator, candle, etc. is determined. Decisions such as sending alerts to designated personnel or agency via short message service (SMS), phone call or by email, or sending commands to the actuators to turn on the environmental control devices.