There are several cheap gas sensors, on the market, of a very simple design. Also, there are sophisticated ones that are ¨Gas Dedicated¨. However, pressure along is not reliable. An infrared( led type) of transmitter should be contemplated with a suitable receiver designed to detect interruptions from the light source. See, leakage has many variants: Sudden and slow-discharging ones. So, depending of the source of gas, you should develop the sensor.

Thank you very much sir. May you please suggest me some research papers or books where I can get detailed suggestions?