MQ-3 Breathalyser

Wave a glass of beer past an MQ-3 ethanol sensor and watch the analog reading swing as the heater catches it.

Difficulty: Breadboard. Estimated build time: about 25 minutes. Estimated parts cost: about US$4.00. 5-part bill of materials with live supplier pricing. A demonstration alcohol detector built around the WINSEN MQ-3 tin-oxide gas sensor — a hot ceramic substrate inside a metal-mesh cage that responds to ethanol vapour by changing its resistance.