The objective of this study were 1) to develop the gas detector unit for installation on Drone and 2) to test the operational sensitivity of the developed device. The development steps included designing complying the electrical circuit testing the electrical system and online connecting system. Besides the operational sensitivity of the developed device was tested comparing the Gas Alert Micro 5 IR the reference gas detector device both in the laboratory and the field site. The results showed that the developed gas detector could detect carbon dioxide carbon monoxide and methane and displayed the results via Line notification every minute. Additionally carbon dioxide detection by MG-811 sensor gave the results similar to the reference device by 95 percent of significant level with the average amount of detected carbon dioxide in the laboratory and the field site were 700-915 ppm and 138-399 ppm respectively. However the measured results of carbon monoxide and methane from the develop device were relatively different to the reference device. Further study on carbon monoxide sensor and methane sensor calibration are recommended.