The instruments utilize an electrochemical fuel cell to measure vaporous
ethanol. As the user blows into the instrument, ethanol is introduced to the fuel cell via a miniature solenoid pump \cite{BACtrack2019a}. Ethanol on the user’s breath is oxidized with the platinum black
coated fuel cell, producing electrons \cite{Wigmore2009}. The
electrical response generated is proportional to the ethanol
concentration on the user’s breath \cite{Jones2019a}.
Users must abstain from drinking alcohol
for a period of at least 15-minutes to allow residual mouth alcohol from recent drinking to dissipate \cite{Anstie1867,Bogen1927,Caddy1978,Gullberg1990,Spector1971}. The instruments do
not have a mechanism to monitor for mouth alcohol, such as those used in
more advanced infrared breath alcohol analyzers \cite{Pon2002}.
To start the testing process, the user powers-on the instrument
and follows onscreen instructions to blow into the device. The user
must provide a breath at a flow rate of 12-14 L/m for approximately 5
seconds, resulting in a total volume of breath provided of approximately
1.2L (email communication, BACtrack® Breathalyzers). The result of the
breath alcohol analysis is shown onscreen to the third decimal in
g/210L. There is no exhalation profile as seen in more sophisticated
infrared breath alcohol analyzers \cite{Wigmore2009}.
After analysis, the app will display a predicted “time-to-sober” (BrAC
of 0.000), based on an ethanol elimination rate of 0.015 g/210L/hr. The
instruments and companion app are programmed to calculate
“time-to-sober” using zero-order kinetics, even when results are below
0.020 g/210L and zero-order kinetics cannot be assumed \cite{Jones2019}. Instruments are programmed for a single breath sample to be
obtained for analysis and cannot be programmed for a duplicate test
sequence. Results can be saved in the smartphone app but cannot be
exported to a spreadsheet for further analysis.