What are the Differences Between Portable and Evidentiary Breath Testing Machines?

Posted by Joseph D. Lento | Jan 10, 2020 | 0 Comments

When police suspect that a driver is under the influence of alcohol or drugs, they will pull them over and initiate a traffic stop. One of the things that the cop is almost guaranteed to do is ask the driver to take a breath test on a breathalyzer.

Not all of these breathalyzers are the same, though. The differences between the breath testing machines used on the road and those that stay in police departments are a big factor in how cases of driving under the influence (DUI) are investigated in Philadelphia.

Preliminary Versus Evidentiary Breath Testing Machines

During the traffic stop, a police officer who requests a breath test only has access to a preliminary breath testing machine. Also referred to as a portable breathalyzer, these are different in three ways from the evidentiary breath tests that are housed in police departments across Philadelphia:

  1. Evidentiary machines are not portable
  2. Evidentiary machines print out the results, while preliminary ones do not
  3. Preliminary breath tests cannot be used as evidence


The most obvious difference between the two is that preliminary breath testing machines are portable, while evidentiary ones are not. Preliminary tests are done on what people tend to think of when they hear the word “breathalyzer” – a hand-held machine weighing less than a pound, with a funnel-shaped mouthpiece.

Evidentiary testing machines, on the other hand, are around the size of the average computer printer. They are unwieldy, heavy, and, most importantly, they need to be plugged into an electrical outlet to work. Because they can't feasibly be taken out on the road, police have to rely on preliminary testing machines, first.

Paper Trail

Breath samples that get analyzed in evidentiary machines in the police department lead to a printed report that includes the breath alcohol content in the sample. Breath tests that are done with a preliminary machine, on the other hand, only lead to a reading on a tiny display screen.

Admissibility as Evidence

Because they produce no paper trail, the results of a preliminary breath testing machine cannot be admitted as evidence in a DUI case. This avoids the tricky situation where a police officer has to remember the reading on the display screen, raising important questions about his or her memory and their credibility.

Instead, the function of a preliminary machine is more to give the officer at the traffic stop an indication that the driver might be under the influence and in need of further investigation. Readings above the legal limit, or even close to it, can be used to justify a decision to make an arrest at the traffic stop and bring the driver into the station for a test on the evidentiary testing machine.

Joseph D. Lento: DUI Defense in Philadelphia

Joseph D. Lento is a criminal defense lawyer who represents the accused in Philadelphia, including people accused of drunk driving. Contact him online or call his law office at (215) 535-5353 for help defending against an allegation that you were driving while under the influence.

About the Author

Joseph D. Lento

"I pride myself on having heart and driving hard to get results!" Attorney Joseph D. Lento passionately fights for the futures of his clients in criminal courtrooms in Philadelphia and across Pennsylvania as well as in New Jersey and nationwide. He does not settle for the easiest outcome, and instead prioritizes his clients' needs and well-being. With unparalleled experience occupying several roles in the criminal justice system outside of being an attorney, Joseph D. Lento can give you valuable behind-the-scenes insight as to what is happening during all phases of the legal process. Joseph D. Lento is licensed in Pennsylvania, New Jersey, and New York, and is admitted pro hac vice as needed nationwide. In the courtroom and in life, attorney Joseph D. Lento stands up when the bell rings!


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Attorney Joseph D. Lento has more than a decade of experience successfully resolving clients' criminal charges in Philadelphia and the Pennsylvania counties. If you are having any uncertainties about what the future may hold for you or a loved one, contact the Lento Law Firm today! Criminal defense attorney Joseph D. Lento will go above and beyond the needs of any client, and will fight until the final bell rings.

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