From the first idea we need to invent a smart gas detector by create application on smart phone to control solenoid valve if gas leaks , when gas leaked but we got advice from commentator “why not close automatically” .Then we charged objective from manual application to cut off automatic. That is the best way to solve this problem and safety. From start the project we learn a lot of new experience such as how to use microcontroller to connect circuit, chemical knowledge about gas properties or safety of life in house and coding in Arduino programs. But we have seen a lot of problems the first problems Firmware of simcom module is not match to ours project, we solve by contract a salesman and send simcom module back to reinstall the firmware, Seconds problems is solenoid valve because solenoids valve use 12volt to make it active but in Arduino board use just 5volt, we solve this problems by buy switch power supply to adapt home electricity from220v to 12v.Furthermore, this project can development or additional in the future because nowadays people are like a comfortable devices to make daily life easily and Technology are always develop. In this project we focus on warning a user and close valve, if have too much gas leaked should reduce gas by open window or leave the house for your safety.