Ways to Fight Breath Test Results in Texas

By January 23, 2019December 9th, 2020Drunk Driving, DWI
Ways to Fight Breath Test Results in Texas

While breath test results aid in establishing probable cause for a DWI arrest in the field, a number of factors can influence results, and reliability can be challenged in court. There are three broad categories of defense – Machine Error, Human Error, and Environmental Factors. Under each of these umbrellas lie multiple ways in in which results can be skewed and therefore inaccurate. 

Inaccurate results mean there are ways a skilled Texas DWI attorney can fight them.

In this post, we’re going to talk about all the things that can potentially go wrong with your breathalyzer test, so that if you are facing charges based on results from one of these fallible handheld devices, you understand that a DWI charge isn’t a conviction.


There are over 100 compounds that may exist in a person’s expired breath that can cause an additive affect to a breath test, and no machine is ever perfect. Even brochure and sales materials for breathalyzers include a margin of error that can reach as high as 14%, and there are a few common issues related to such a wide range.

Semiconductors – The semiconductor sensors in breathalyzers are known to be subject to false positives from common non-alcoholic substances such as ketones. So, those on low-carb diets could register a false positive if tested. Those with diabetes who are asked to take a test are more likely to register a false positive, as well.

Foreign Substances – Alcohol vapor emitted from substances present in the mouth can produce false positives when the amount is greater than what is exhaled from the lungs. Mouthwashes, breath fresheners, and toothache medicines contain alcohol and can skew readings. Foods infused with alcohol or foods like homemade bread can also show as a BAC presence. Even smoking cigarettes can make a test read higher than alcohol alone.

Solids to Liquids Ratio – From a chemistry standpoint, the ratio between solids and liquids in the blood naturally vary – often widely so – from person to person. When a greater amount of blood solids than aqueous content is present in a given subject’s blood, that BAC will appear higher than a person with less blood solids content. Normal variation in study subjects has reflected a huge margin of error (10-14%).

Nerves – Something else a machine is unable to account for is the breathing patterns of a nervous person taking the breathalyzer test. Holding your breath prior to blowing has been proven to produce more volume of air and warmer breath – both of which are conducive to higher results. If you are nervous or waiting for the administering officer to say “go,” you are likely to hold your breath for some period just before exhaling into the machine. In turn, your BAC results may register higher than if you were simply breathing normally. 

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False results can be triggered by the presence of paint fumes, varnish, and chemicals such as plastics and adhesives. Granted, the likelihood of being asked to take a breathalyzer test while surrounded by these kinds of fumes is slim, but it has happened. Other, more common environmental factors include:

Temperature Variation – One of the foundations of breath testing science requires that temperatures both inside the body and out should be the same, and constant. However, studies have shown that the average temperature of expired breath is typically about one degree different than the air outside the mouth (where the device is actually using the temp as a benchmark), resulting in about an 8% overestimation of BAC compared to blood. 

Radio Frequency Interference (RFI) – Believe it or not, current-day handheld devices are calibrated based on avoiding interference from radio frequencies used in the 70s and 80s. The RFI detectors in them are also rarely calibrated using more than a single calibration device. It is common knowledge that band widths are now much different, and frankly more numerous than 40 or 50 years ago. Lastly, devices are often tested in a lab based on those outdated wavelengths, often without using a real test subject. 


Although the use of breathalyzers has become a standard part of law enforcement training for field sobriety tests, and police officers are actually required to be certified to conduct them now, the administrative rules only set out a minimum requirement, and the guidelines must be followed to the letter in order to garner anything near to accurate results. Failing to observe the proper 20 minutes, changing a mouthpiece, labeling independent sample tubes, inputting incorrect serial numbers – all can render results unreliable, inaccurate and inadmissible. For example, here are two very common errors:

Calibration – A machine must be calibrated periodically, and batteries must be replaced in order to maintain accuracy. Over time, its sensor becomes saturated, and the results of the device can drift. Think of it like resetting a clock.

Consistency – To ensure accuracy, breath tests should be performed multiple times to produce reliable results. Those utilizing fuel cell sensor technology provide the most reliable and accurate results in repeated tests.

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There is no doubt, breath testing is a breakthrough technology that has prevented countless accidents and fatalities, and we don’t believe the test is going anywhere.

However, this kind of testing in the field, no matter how meticulous the administrator may be, is fallible in countless ways, and in this post, we’ve only covered a few. If the prosecutor in your case is trying to use the results of your breathalyzer test against you, this is something that can and should be fought.

About the Author: 

After getting his Juris Doctor from the University of Houston Law Center, Jeff Hampton began practicing criminal law in Texas in 2005. Before becoming a defense attorney, he worked as a prosecutor for the Tarrant County District Attorney’s Office – experience he uses to anticipate and cast doubt on the arguments that will be used against his clients. Over the course of his career, he has helped countless Texans protect their rights and get the best possible outcome in their criminal cases. His skill has earned him recognition from the National Trial Lawyers (Top 100 Trial Lawyers) and Avvo (Top Attorney in Criminal Defense, Top Attorney in DUI & DWI, 10/10 Superb Rating), and he is Lead Counsel rated. 

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