NOVELTY - The system (100) has a gas measuring device (200) comprising a chamber (202) with an air cell and an opening. A sensor (206) is placed in the chamber for receiving light emitted by a light source (204) correspondingly. A processor (208) is electrically connected to the light source, the sensor and a connection port (210), for controlling the light source to emit the light according to a control signal, such that the sensor generates a sensing signal. The processor receives and processes the sensing signal, and outputs a characteristic value to a computer device (300).    USE - Gas detecting system for detecting property of gas in an external environment and in a gas container. Uses include but are not limited to carbon dioxide, carbon monoxide, methane and ozone.    ADVANTAGE - The chamber comprises a fan for increasing flow rate of the gas of the external environment flowing into or out from the air cell, so that the detection time can be shortened. The system comprises a reflective layer, where the intensity of the light received by the sensor is increased, thus improving the sensitivity of the sensor. The system comprises an arithmetic unit for generating driving signals through a control procedure, so that process of gas detection and time of gas detection are effectively controlled. The system prolongs service life of the light source, and saves power, as the light emitted by the light source is pulsed light, and the light is completely absorbed during non-detection time. The system can detect multiple gases, simultaneously, through the selection of the light source and the sensor. The system comprises an alarm to warn a user that the external environment is dangerous when the concentration of the gas detected is excessively high. The system allows the user to manage the average concentration and the total concentration of various detected gases of the external environment in a period of time. The light emitted by the light source is passed through the air cell when the gas measuring device performs gas measurement, and is passed through the reference air cell simultaneously incident into the four sensing units of the sensor, where a signal sensed by one of the four sensing units after the light is passed through the reference air cell, can be used to modify signals sensed by the three sensing units after the light is passed through the air cell, so that error generated due to the interference of gas flow can be reduced.    DETAILED DESCRIPTION - The computer device is a notebook computer. The connection port is a Universal Serial Bus (USB) interface. The light source is an infrared IR light source. The sensor is a non-dispersive infrared sensor. An INDEPENDENT CLAIM is also included for a gas detecting method.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of a gas detecting system.    Gas detecting system (100)    Gas measuring device (200)    Chamber (202)    Light source (204)    Sensor (206)    Processor (208)    Connection port (210)    Computer device (300)