A breathalyzer is a machine that is commonly used in a DUI investigation to further the suspicion that someone is under the influence. This is also evidence that is retained for a later time to prove that someone is under the influence or above a 0.08. If you have been charged with drinking and driving and want to discuss your breathalyzer results, call Ozols Law Firm today for a free consultation.This guide will explain to you the common defenses to beating the breathalyzer.

Defenses to Breathalyzer Results

Partition Ratio

The ratio of breath alcohol to blood alcohol, also known as the partition ratio is 2,100:1. This means that 2,100 milliliters (ml) of air in the lungs will contain the same amount of alcohol as 1 ml of blood. Remember, when the breath test is the only form of evidence that means that the prosecutor is making a conversion by taking the amount in your breath and trying to equate that to the amount of alcohol in your blood.

Every person is different and there are multiple factors like sex, age, weight, and how often one drinks, that determine their partition ratio. The prosecutor uses a general ratio as an assumption or a hypothetical and this number needs to be challenged so that the jury can be shown that they cannot just convict someone on a hypothetical assumption.


As discussed here, absorption and absorption rate is a phrase that an expert will often use to try and confuse the jury. How do you use this as a defense? By getting educated on this factor or hiring an attorney that knows all about what these numbers really mean. A skilled DUI attorney will be able to do the calculations right there in front and the jury and make the alleged “expert” stumble when they have to admit the numbers they were using were inaccurate, which produced a completely inaccurate calculation.


Again, elimination is the same theory as absorption rate. How can someone just go on the witness stand, without any other information and provide testimony on what someone’s elimination rate is? These experts were not there when the individual was drinking, they did not see them drink, they don’t know for a fact what type of alcohol they drank or how fast they drank it. All of this information needs to be shown to the jury. They need to be questioned on their numbers and their assumptions. Without all of that information no one can logically calculate an elimination rate, and without an elimination rate, it cannot be calculated what the individuals BAC was at the time of driving.

User Error

User error is actually something that is more common than expected. User error is when the police officer makes a mistake while using the breathalyzer device. These machines are actually not as straightforward as expected and often the officers will only be trained for a short period of time and not always comprehend what they have learned. They then reinforce their incorrect and bad habits every time they take a test. User error is something a skilled dui attorney can spot immediately and then use their own skills to question that officer on the witness stand and make sure that information is portrayed to the judge and the jury.

Title 17 California Code of Regulations

Title 17 is a number of rules that have been set out by the state of California in order to show what is a proper operating standard when administering these tests. It sets out rules and training obligations that everyone must follow and it also sets out maintenance requirements as well. For example Title 17 says that the 2 breath tests that are taken must be within 0.02 in order to be a valid test. These officers and forensic alcohol supervisors are only human and often make mistakes. ANY mistake in your case could mean a dismissal or a not guilty verdict and any violation of Title 17 needs to be found and dealt with immediately.

15 Minute Observation Period

The 15 minute observation period is something that is required by Title 17. It says that before a breath test an officer must observe the individual for 15 minutes. This means that they have to watch to see that they do not burp, regurgitate, vomit or smoke within that time. It should also be shown that they are not chewing gum or any type of substance in their mouth that can compromise the breath test. Most officers do not do the 15 minute observation period and will often just do paperwork in that time or talk to other officers. The observation period should start by looking in the individual’s mouth and have a constant observation for the smallest burp or regurgitation of food. This rarely occurs and needs to be exploited in order to beat the breathalyzer test.

Radio Frequency Interference

Breathalyzer devices are essentially computers and they have working components that can be interfered with. The Intoxilyzer EC/IR’s instruction manual clearly states it should not be used around radio interference as it could affect the results of the test. The Intoxilyzer even has a built-in device to try and block radio interference because in previous models this was becoming a serious problem. Again any top DUI attorney in San Diego can quickly find out whether the officers had their radios or cellular phones while they were taking this test and bring in evidence that it caused a problem with the breath testing results.


To calibrate a breathalyzer essentially means to make sure that everything is set to a certain standard. On machines where it is calculating certain numbers or percentages, the machine needs to be checked often to see if the target control range is still in the range with an allotted margin of error. On the Intoxilyzer EC/IR it is recommended that the “Alcohol Standard (wet bath)” in the system not exceed 15 days or 50 tests. The Dry gas does not have a day range but needs to stay within a certain range of PSI to be working properly.

In San Diego, it is common that they give a calibration packet, which certifies that it has been calibrated sooner than 150 tests. A lot of inexperienced attorneys will just take this at face value and think, “because the police wrote this it must be true”. In the business of criminal defense, that is rarely the case. There is a lot more that goes into calibrating a machine than just writing that it was done on a piece of paper. Often the DUI expert that the prosecutor provides will know nothing about how the machine worked, and will not be able to testify whether it was calibrated properly, leaving the jury to wonder whether the case is really as strong as they thought it seemed.

Diabetes/Low Carb Diet

Diabetes and/or a low carb diet can certainly affect the breathalyzer machine and there have been studies where someone with no alcohol on their system blew a 0.01 just from their low carb diet alone. For more information please refer to San Diego DUI Attorney Alex Ozols’ blog post.

Retrograde Extrapolation

Retrograde Extrapolation is essentially a theory of calculating the blood alcohol level back in time to the time the individual was driving. Remember, VC 23152 (b) states that the driver of the vehicle must have been above 0.08 at the time of driving, not when the test was taken often hours later.

This is something that a DUI attorney can use to their advantage. If a client has a BAC done by a breathalyzer that was a 0.09 and it was done a couple hours after driving then it can be argued that when they were driving their actual BAC was a 0.06 and it rose to a 0.09 within that time. If their BAC was a 0.07 at the time the test was taken and the prosecutor tries to argue that it was higher hours before, then any criminal defense attorney can use their own calculations to poke holes in that theory and show that the theory is invalid.

These are the tricks of the trade and the ways to get a DUI breathalyzer case dismissed or obtain a not guilty verdict. Only the most experienced DUI lawyers have perfected these strategies to obtain the most possible results for their clients.