How Reliable Are Breathalyzer Machines in Maryland DUI Cases?

 Posted on March 08, 2026 in DUI Defense

If you were pulled over for DUI in Maryland and failed a breathalyzer test, you may assume the case against you is airtight. It isn't. Breathalyzer machines are widely used by law enforcement, but they are far from perfect. A failed test does not automatically mean a conviction, and our College Park, MD DUI defense lawyers know how to challenge breathalyzer results in court.

How Does a Breathalyzer Test Work?

A breathalyzer does not directly measure the alcohol in your blood. It measures alcohol vapor in your breath and uses that measurement to estimate your blood alcohol concentration (BAC). The problem is that breath and blood are not the same thing, and the conversion the machine uses can produce results that do not accurately reflect your actual BAC.

There are two types of breath testing devices used in DUI cases. The first is a portable breath test (PBT), which is a small handheld device used roadside. In Maryland, under Md. Code, Transportation 16-205.2, results from a roadside PBT cannot be used as evidence against you in court. They can only be used by the officer to decide whether to make an arrest.

The second type is the evidential breath test (EBT), administered at the police station. This is the result that prosecutors typically rely on in court.

How Accurate Are Breathalyzer Machines?

Even the more reliable station-based machines have known limitations. Studies show breathalyzer error rates can reach as high as 20 percent, meaning a reading of 0.08 percent could actually reflect a BAC anywhere between 0.064 percent and 0.096 percent.

That margin matters because 0.08 percent is the legal limit for DUI in Maryland. Someone who tests at exactly 0.08 percent could have an actual BAC well below the legal threshold.

What Can Cause a False or Inflated Reading on a Breathalyzer Test?

A number of factors can push a breathalyzer result higher than your true BAC. These include:

Improper calibration or lack of routine maintenance on the device

Alcohol detected from mouthwash, breath spray, or cough syrup used shortly before the test

Medical conditions like GERD or acid reflux, which can push stomach alcohol vapor into the mouth and inflate readings

Diabetes, which can cause elevated acetone on the breath that some devices read as alcohol

Officer error in administering the test or failing to observe the required waiting period before testing

Each of these issues can form the basis of a challenge in your case. Your attorney can request calibration records, maintenance logs, and the officer's training history to look for weaknesses in the prosecution's evidence.

Can a Judge or Jury Reject a Breathalyzer Result?

In Maryland, a judge or jury is not required to find you guilty simply because you blew over 0.08 percent. The result is one piece of evidence, not a guaranteed conviction. If your attorney can show that the machine was poorly maintained, improperly operated, or that a medical condition affected your reading, the court may give that result less weight or exclude it from consideration entirely.

Blood tests are generally considered more accurate than breath tests, and if there is a significant difference between your breathalyzer reading and a blood test result, that discrepancy can be a strong point in your defense.

An experienced DUI defense attorney knows how to dig into the details behind a breathalyzer result and challenge the evidence that the prosecution is counting on. The sooner you get an attorney involved, the more time they have to build that challenge before your case goes any further.

Schedule a Free Consultation With Our Rockville, MD DUI Defense Attorneys

A breathalyzer reading is not the end of your case. There are real and effective ways to challenge this evidence, and the outcome often depends on how quickly you act. At Arrested for a DUI, LLC, we have more than 30 years of combined experience that help us fight for our clients with every DUI case we handle.

If you've been charged with DUI, call our College Park, MD DUI defense lawyers today at 301-479-5466 to schedule a free consultation. Se habla Español.