Strategic Defense
From A Former Prosecutor

Can a breath test give a false reading?

On Behalf of | Jan 11, 2024 | Drunk Driving

Breath tests are a widespread tool for law enforcement to measure blood alcohol concentration during traffic stops. While these tests are efficient in detecting alcohol levels, questions arise about their accuracy.

Many drivers accused of a DUI wonder if a breath test can give a false reading. Understanding the inner workings of a breath test can help you stay informed and build a proper defense against a DUI accusation.


One key factor influencing the reliability of a breath test is the calibration of the device. Like any other instrument, breath test devices require regular calibration to ensure accurate readings. If a device is not calibrated correctly or if it malfunctions, it can produce false results. Law enforcement agencies typically have protocols in place for routine maintenance and calibration, but errors can occur.

Individual variations

Human physiology varies widely, and this plays a significant role in breath test accuracy. Factors such as body temperature, metabolism and medical conditions can impact the results. For instance, individuals with diabetes or certain respiratory conditions may produce higher breath alcohol levels even when their actual BAC is low.

Mouth alcohol contamination

Breath tests rely on the assumption that the alcohol measured originates from the lungs. However, if there is residual alcohol in the mouth, it can lead to an inflated reading. This can occur if a person has recently consumed alcohol, used mouthwash or even ingested certain medications. To mitigate this risk, law enforcement officers often observe a waiting period before administering the test.

The latest data from the California DMV shows that 2019 saw a DUI arrest rate of 455 arrests per 100,000 licensed drivers. For each of these arrests, a breath test was a likely measure in determining whether the stopped driver was truly under the influence at the time. The possibility of a false reading can lead to some drivers being wrongfully accused of a DUI offense.