New Jersey police, like police in all other states, use a device to determine the amount of alcohol in a driver’s blood stream – blood alcohol content or BAC – so that they know whether to arrest the driver for driving under the influence of alcohol. The device most commonly used to make this determination is called a “breathalyzer.” Most people, however, do not know how these devices can determine a person’s BAC by taking a breath sample.

The suspect is usually asked to breath into the mouthpiece on the breathalyzer. Alcohol is not digested upon absorption by the lungs or modified in the bloodstream. Some of the alcohol will move across and through the alveoli membranes in the lungs and enter the bloodstream. It is present in a person’s breath when he exhales.

The breathalyzer contains two glass vials that change color when exposed to alcohol molecules, and a system of photocells that measure the color change in the vials. When alcohol is passed through one of the vials, the liquid changes color based upon the amount of alcohol in the sample. The photocells then pass electric currents though the liquid in each vial. The amount of current that passes though the vial depends upon the color, which in turn depends upon the concentration of alcohol in the vial. The photocells pass an electric current to meters on the front of the breathalyzer, and these meters provide a measure of the suspect’s BAC.

An intoxilyzer uses infrared spectroscopy instead of electrical current to measure the suspect’s BAC. Infrared light is passed through a sample of the suspect’s breath. Alcohol will absorb infrared light, and the amount of light absorbed by the suspect’s breath provides a measure of BAC.

Breathalyzers and intoxilyzers are sensitive scientific instruments, and they must be carefully adjusted to provide reliable results. Experienced DUI defense attorneys are familiar with how various events, including the failure to calibrate the devices, can influence and distort the readings produced by a breathalyzer. Anyone who has been charged with DUI based upon the reading from a breathalyzer or intoxilyzer may benefit from consulting a lawyer with experience in defending such charges. A capable attorney can evaluate the evidence, suggest potential defense strategies, and, if appropriate, negotiate an acceptable plea agreement.