The Keychain Breathalyzer is really a great value, but like any measuring device, you HAVE to understand a little science and how to properly use it. When I first got this little doodad, I put the battery in and went hog playing around with it, drinking with some buddies. The next day, it started acting really funny. It would turn on and start counting down, and then shut off almost immediately. If I left it alone for several hours, I could do a test, but then it was unable to do another test. Sometimes I could do a test and it gave me the 'Lo' message. I thought the battery was dead. I checked the battery with a volt meter, and the battery didn't look dead at all. I thought I got a lemon... and then I got a new battery. Now it's fine. To those who have seen the "it was working great the first night, and then it quit on me" reviews, this is what's going on: RELIABILITY: This device seems power hungry, and I have a feeling that the AAA battery can't immediately produce the power it needs, so it needs to harvest the energy slowly while not in use so that it can do a test. I didn't like that this behavior isn't explicitly explained in the manual. The manual does say to wait a few minutes between tests. If you don't follow this, it will actually kill the battery. If you played with it non-stop all night and it won't work anymore on a seemingly good battery, replace the battery and use it properly. It will function perfectly. This is something that should be clearly addressed in the manual, and I think would eliminate the negative reviews that I have seen. Realize, this device was designed for a responsible drinker who wants to stay safe. That person will use it perhaps 4 times at most throughout an evening. ACCURACY: I've never been able to measure and track the phenomenon of BAC, so I had no idea what to expect. I looked at a table of BAC's, drink units, and body weight/height to see what a standard drink should do to me. I did a proper test, where I had 1 drink unit (1 12oz can of beer in this case) and waited 20min to do a test. It matched the table perfectly. And it's very consistent. If I repeat a test, it is always within 0.01 of the last. You don't necessarily have to wait the full 20 minutes, but there are caveats. If you are still absorbing alcohol in your GI tract, yet have absorbed all of it in your mouth and throat (you ate a big meal before drinking), the reading will be low because you haven't absorbed everything into your system yet (it will continue to rise even if you don't have another drink). If you're still absorbing alcohol in your mouth (ie. after a sip of hard liquor), it will read high because the alcohol takes longer to absorb through your mouth and throat. You can rinse your mouth and do a test to get a ROUGH idea anytime, but if you want to be sure about your reading, wait 20 minutes. If 20 minutes isn't possible and it's important, your environment isn't healthy. CALIBRATION: The official website says that it should be sent for calibration after 6mo - 1yr. Closer reading of the manual confirms what many professionals in the BAC field will say: Every Month. The manual states that under 'average' use, it will need to be calibrated after 6mo - 1yr. But under daily use, it may need calibration as often as once a month. I will periodically see what it reads my BAC 20 min after 1 standard drink, and send it off when it looks inconsistent or off. CONCLUSION: BAC was a much simpler concept in my head until I started reading and got this doodad. You have to learn a little science to understand what is going on. But it will help you understand that "feeling OK" is often not good enough. Really, this tool is most useful if you understand how alcohol interacts with your body. Breathalyzers are not a surefire or definitive way to measure 'drunkenness' because they are an indirect measurement that can be affected by many factors. However, if you would like a tool to give you a rough idea of what you can handle, and have the knowledge to understand what factors are at play, it's a damned educational gadget that I would recommend to anyone interested in some learnin'. At $30, it's a great deal. If you need more accuracy, or whatever, spend the money for a fuel-cell breathalyzer and get it calibrated every month. The BACtrack keychain is a good "back of the envelope" tool that can be very educational.
