I teardown a commercial, handheld breathalyzer and discuss how it works, then test a standalone ethanol sensor. http://www.seeedstudio.com/depot/images/product/MQ303A.pdf http://www.kosmodrom.com.ua/pdf/MQ303A.pdf http://www.sparkfun.com/products/8880 http://www-personal.umich.edu/~mswool/publications/Gas_Sensors_preprints.pd.pdf