Gas sensor MQ9 for Arduino:
It detects the presence of CO (Carbon Monoxide), CH4 (Methane) and LPG in air. The best results are given when alcohol is in liquid form, however, it still does an amazing job when measuring in gas form. It needs a bit of time to warm up in order to work correctly.
• Detects: CO(Carbon Monoxide), CH4(Methane), LPG
• Dimensions: 32mm x 22mm x 27mm
• Voltage: 5V
• Digital(HIGH/LOW) and analog(0V-5V) output
• With LM393 comparative
• Comes with soldered 4-pin male header