I got one of them Drink Shields and assembled it today. It uses a Alcohol Gas Sensor MQ-3 to take readings and displays them on a light bar that goes up to 11. No idea how to convert this to BAC but one beer didn't even push one led a few minutes after drinking. The datasheet says it needs a 20 hour burn in before the sensor becomes reliable so we'll have to see.
My blog about me and my resulting life.