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The Alco-Sensor

The Alco-Sensor is the portable, hand-held device law enforcement uses, at the scene, to test for the presence of alcohol on a person’s breath. The test is performed, roadside, by having a suspect blow into a tube attached to the device the officer will hold in his/her hand. The device then produces a digital reading displaying your BAC (Blood Alcohol Content).


No, and for a lot of reasons. Gauging BAC based on a person’s breath is highly suspect to begin with. To make matters worse, the Alco-Sensor is not nearly as sophisticated as the Intoxilyzer machine which is used (typically at the jail) after an arrest is made. Furthermore, the ones in service are rarely re-calibrated and are usually mistreated by the officer using it. For example, many officers simply toss the Alco-Sensor in the trunk of their patrol cars following use and don’t bother retrieving it again until it’s needed the next time.


Yes. The Alco-Sensor is a preliminary screening device used by officers to determine if the clues present are the result of alcohol or, possibly, some other substance.

However, the officer may only testify as to the general result of the test. Because of its horrible inaccuracy, the Alco-sensor cannot be used to show the BAC of a suspect. In other words, the prosecutor may not ask, nor may the police officer testify as to, the numerical read-out on the Alco-Sensor. He/she may ONLY state that you tested positive or negative for alcohol. That’s it!

Of course, this is meaningless if you’ve already admitted to having had a beer or two. If you've denied drinking, this test can make you look like you have something to hide.


First, an officer should only administer the Alco-Sensor test AFTER you have taken your 3-part Field Sobriety Test. Why? Because the purpose of the Alco-Sensor is not to gauge impairment. Its sole purpose is to confirm whether or not the clues observed during your Field Sobriety Test are due to alcohol.

Should the officer administer the Alco-Sensor before your Field Sobriety Test, a high numerical read-out may create a “confirmation bias” in the officer’s mind. In other words, the investigating officer might then see clues which really aren’t there solely because he/she saw a higher-than-legal BAC on the Alco-Sensor.

Unfortunately, this does not make the results inadmissible, but it makes the officer impeachable for his/her failure to follow his or her training and it should make the results of your Field Sobriety Test, as perceived by the officer, less reliable. A good DUI attorney knows how to utilize this evidence in your favor.

If you, or someone you know, has been charged with DUI, please visit my website at You can contact me via email at [email protected] or by phone at 770-729-4809.

-        Jason Carnell

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