What a waste of money! Compared the results with a professional (police-issued) breathalyzer, and it was not even close! The mfg. says it may need to be calibrated from time to time, but calibrated when it's right out of the box - ridiculous. The difference between the Alcohawk and the professional breathalyzer was a FULL POINT. Not off by .02 or .03; a full point.