Ah, alcohol. Regular readers will recall me getting excited by new fuel cell technologies, where you pour a miniature of vodka into the back of the cellphone and it runs for longer than you would on the same supply. This is getting darn close to production now, so researchers are looking for new uses already and they've realised it makes a pretty good breathalyser. Pump some air from a car's cabin through one of these cells, and if it generates a voltage you've got alcohol in the atmosphere. No blowing into the bag required although that would surely follow if the light goes red on the first test.
A fine idea, and I look forward to similar ideas to warn the unwary if their garlic breath is at a dangerous level or whether the deodorant's worn off yet. Technology will make civilised beings of us all, in the end.