In Wisconsin, it is unlawful to operate a vehicle if you have a blood
alcohol concentration (BAC) at or above 0.08%. While officers can smell
your breath and monitor your actions, they are likely to want to gather
more concrete proof of your BAC. Asking you to breathe into a testing
device is how the police try to achieve this goal.

Alcohol breath testers should correctly measure your BAC by analyzing the ethanol content in your breath. They do not measure nicotine, but ethanol in ejuice can lead to false positives.
Regrettably, that is not always the case, as many factors can lead to
false-positive results. These include the foods you eat, the medical
conditions you have and the medications you take. Vaping may also cause
you to fail an OWI breath test.

E-liquids may contain ethanol

A recent study from Virginia Commonwealth University found the
e-liquid that goes into electronic cigarettes often contains ethanol,
which is a type of alcohol. In fact, out of 56 e-liquid samples
researchers tested in the study, only three did not have ethanol. Even
more alarming, many of the tested e-liquids contained 10% or more of it.

Ethanol registers on breath tests

While the ethanol in e-cigarettes is not likely to be sufficient to
drag your BAC over the legal limit, residual ethanol in your mouth may
register during a breath test. If you vape shortly before or during your
OWI stop, the testing device may erroneously believe your BAC is 0.08%
or higher.

It is not illegal for most Wisconsinites to use e-cigarettes, of
course. Ultimately, if you can prove a testing device gave an
erroneously inflated reading because of your vaping and not your
drinking, you may have a valid defense against the OWI charges you are
facing.