I carry this in my vehicle and when I attend an event (like a tailgate party before a sporting event for example) I wait the instructed 20 minutes after drinking a beverage (non or alcoholic) and/or food and use the Bactrack...readings are consistent and I've often had to wait it out before driving probably saving me a career-ending DUI as a result. Total piece of mind. I follow the instructions verbatim and am about to send it back for the must-do recalibration.
This was purchased a little over a year ago. The battery has held up, the calibration went fine. The only thing I didn't know is if the item is not mailed in right away after the online order, you have to start another order or get another number to pay for this process.
Never worked correctly, but I think that's my fault (not waiting 20 min after drinking) sent off for calibration, other than having to deal with Canada post, everything went well