Gas primarily consists of 50% hydrogen, 35% methane, 10% carbon monoxide, and 5% ethylene. In the case of gas leakage alone, the concentration of carbon monoxide may be relatively low and might not be sufficient to trigger the alarm. Only when the gas is not completely burned will a significant amount of carbon monoxide be produced. 

 Please note that the alarm will only be triggered when the concentration of carbon monoxide in the air reaches the alarm threshold. If the carbon monoxide concentration is below the alarm threshold, the alarm is typically not activated.