The purpose of this research is to design, develop and test the functionality of the carbon monoxide gas leak detection system prototype. Carbon monoxide is a tasteless, colorless and odorless gas produced by running engine, the accumulation of carbon monoxide caused by leakage from exhaust system to a car cabin compartment reduces the oxygen levels unnoticeable. Absence of detector system in the consumer vehicle might cause a fatal incident to driver and passengers in the worst case. Based on design thinking steps, this prototype was developed using NodeMCU ESP8266 as a microcontroller to assists users by displaying current readings of carbon monoxide gas and warns users about the leakage of carbon monoxide gas is on risk level. Analysis shows that this prototype capable of detecting the presence of carbon monoxide gas based on three stages; first (151ppm - 400ppm), second (401ppm - 800ppm), the LED will turn on and the LCD will display readings, third, if the gas exceeds 800ppm, the LED will be lit, the buzzer will mark a sound for 10 seconds and the LCD will display the current reading of carbon monoxide gas. After 10 seconds, if the prototype not be turned off by the users, the information will automatically be sent to the Department of Fire and Rescue Malaysia Twitter account.