To use your BreathKey, simply press the button on the front of the device. Your last BAC reading will be displayed, and then WAIT will appear for a few seconds. Next you will see BLOW, at which point you blow for about 4 seconds, until you hear a long beep.
It’s important that you blow with moderate force until you hear the beep. Not blowing long enough or forcefully enough can cause the BreathKey to abort the test and make you start over. Blowing for a full 4 seconds makes sure that the BreathKey will take a deep-lung sample of your breath so that it can provide the most accurate reading.
You will again see WAIT for a few seconds while the device calculates your BAC. Finally, your BAC level will be digitally displayed. After about 10 seconds the device will turn itself off. (see “How does it work”)
As is the case with any breathalyzer, you first must wait about 20 minutes after your last alcoholic drink for the alcohol in your mouth to dissipate and be absorbed into your system.
A breathalyzer analyzes the alcohol content in your lungs. If you use a breathalyzer immediately after having a drink, the alcohol that remains in your mouth will be blown directly into the breathalyzer. The breathalyzer will then result in a much higher blood alcohol content (BAC) reading than it would if the alcohol had passed through the stomach and intestines, into the bloodstream, and into your exhaled breath (see “How do breathalyzers work?“).
Note that items such as breath spray or mouthwash contain alcohol and these items may result in a higher BAC reading. Waiting 20 minutes after using either of these will allow the alcohol they leave in your mouth to dissipate before testing.