I had bought this device from a local retailer, hoping to use it as practical party favor and for assisting myself and friends to determine whether we were below legal tolerances for driving. I met with some friends at a bar and we proceeded to start testing the device, following the directions to the letter, -and despite that- the readings would vary depending on not only how forcefully you blew into the sensor, but also how far your mouth was; even varying minor distances. This product is NOT fit for consideration or for accurate readings, not to mention the cheap quality feel of the build materials. Thankfully I was able to return it, but for those browsing; the device shouldn't be trusted for more than a dollar; and even then the money would be better spent towards another pint.