Introduction to Methods for DUI Detection used by Law Enforcement

What is DUI?

introduction to methods for dui detectionA driving under the influence charge is a criminal offense that includes either driving under the influence of alcohol or drugs to an extent that it impairs your physical and mental abilities to operate a vehicle.[i] Every state has their own DUI laws, including a range of penalties if convicted. One thing that is standard across all 50 states is that the blood alcohol level of the driver must not exceed 0.08%.[ii] In Arizona, there are three classifications of DUI charges which are all based on the blood alcohol concentration level at the time the driver was pulled over.

A standard DUI conviction in Arizona is classified as driving a vehicle with a blood alcohol concentration blood alcohol concentration of 0.08% or more in a standard vehicle.[iii] A standard DUI conviction for a commercial vehicle is much lower, at 0.04% BAC.[iv] While some states allow a small blood alcohol concentration for underage drinkers, Arizona has a no tolerance policy for this. If ANY alcohol is detected in the underage drinker, it can result in a DUI.[v]

The next type of DUI is an extreme DUI. This is classified as driving with a BAC of 0.15% or higher. Finally, an aggravated DUI in Arizona can arise under three different situations.[vi] First, an aggravated DUI can arise if the DUI was committed while the driver’s license was either suspended or revoked.[vii] Next, if the DUI was the third offense for DUI within 84 months.[viii] And finally, if the DUI was committed with a child under the age of 15 years, the DUI will be classified as aggravated.[ix]

Overview of Methods for DUI Detection

Since the three classifications of the DUI offenses are based upon the blood alcohol concentration of the driver at the time he was pulled over, law enforcement must have a means of detection in order to make a proper arrest. Since it is impossible to know exactly what a person’s blood alcohol concentration is by looking at them- especially through a moving vehicle, there are numerous methods available for law enforcement.

Probable Cause to Stop a Driver and Field Sobriety Tests

First of all, a police officer may pull over a driver for any reason – if they have probable cause. Probable cause in layman’s terms means that the police officer has reliable information to support a reasonable belief that a person has committed a crime.[x] Driving under the influence of alcohol or drugs is a crime, so if the police officer has reason to believe the driver is impaired – they can pull them over. Some tale tell signs of impairment while driving, that police offices look for, include: problems in maintaining proper lane position – swerving frequently, speed and braking problems, vigilance problems, and judgment problems.[xi] While some people are just bad at driving and these are typical problems for them, these are standard signs of impairment while driving and the driver is at risk of being pulled over if law enforcement witnesses this. If the driver is not impaired, they may still face some tickets based off such poor driving skills.

field sobriety tests as one of the methods for dui detection by law enforcementNow, one way a police office may test to see if a driver is impaired with alcohol or drugs in their system is a field sobriety test. This test is also referred to as a roadside sobriety test and is typically used before any other forms of testing the blood alcohol concentration of the driver. The field sobriety test is a standard three part test. The first test is called the Horizontal Gaze Nystagmus.[xii] The police officer will ask to driver to follow his finger with his eyes, while the officer moves his fingers from left to right. This is the test that police officers use to detect whether or not the driver’s eye involuntarily jerks.[xiii] This jerking is called nystagmus and it is exaggerated when a person is intoxicated.[xiv] When the officer performs this examine, they are looking for three major things that the driver’s eye would do if they were impaired. First, they will look to see if the driver’s eyes are able to smoothly follow a moving object. Second, the officer will look for eye jerking when the eye is dilated- from the officer shining their flashlight in the driver’s eye. Finally, the officer will look for the eye jerking within 45 degrees of the center.[xv]

The next test the officer will ask the driver to perform is the walk and turn test. The office will ask the driver to take nine steps, heel to toe, and then turn around and repeat.[xvi] While this is an easy task for an unimpaired person, it can be quite difficult for someone under the influence of alcohol or drugs. Finally, the officer will ask the driver to stand with one foot about six inches off the ground and ask the driver to count for thirty seconds.[xvii] While some people struggle with balance, generally this is not a hard test for a sober person.

Those three tests are the most common field sobriety tests that police officers use, but other tests can be used to also detect if a person is impaired. For example, a police office may ask the driver to say the alphabet or count the fingers the officer raises. Now, the officer may make the arrest based off those tests, or they may use other methods of detection, just as the breathalyzer tests.

Breathalyzer Tests

A breathalyzer test is an analysis testing device that can detect blood alcohol concentration after the person blows into the machine.[xviii] The breathalyzer test is a strong piece of evidence against the driver of their blood alcohol concentration – but the test must be properly administered. Every breathalyzer device must be properly maintained and calibrated before each and every use.[xix] If the device is not properly maintained, the results of the test could be skewed and not be eligible for use against the driver.

breathalyzer as one of the methods for dui detectionWhile every state has their own specific ways of maintaining the device, there are a number of generally standard practices of maintenance. These include: the device itself must be on a list of conforming devices, the device must be checked at regular intervals, the person administering the test must be certified to use the device and the person must administer the test in accordance with his training, and the person administering the test must ensure the person taking the breathalyzer test does not burp, eat, smoke, or vomit directly before the test.[xx] The person administering the test must also administer two tests and the results must produce readings that are 0.02 of one another.[xxi] If the driver can prove that any of those standards were not followed, the court may not allow the results to be used against the driver. It is very important that person or police officer administering the test to ensure that every step of standard maintenance to take place with the breathalyzer device to ensure it can be used against the driver.

Blood Tests

Another test that can be used to detect the blood alcohol concentration is to administer a blood test on the driver. It is a common procedure, but police officers are unable to perform the test while roadside.[xxii]  Every state has their own laws to regulate blood tests, including any necessary required training and standard procedures. Blood tests are able to detect a lot more than just alcohol.[xxiii] Blood tests are able to detect a wide array of both legal and illegal drugs.[xxiv] Intoxication while driving is not solely based off alcohol consumption, and there are just as many consequences as driving while high as there is as drunk. A blood test will allow law enforcement to narrow down the exact source of the intoxication and as such, the police officer will be able to make the appropriate arrest.

Check Points

While not all states permit check point stops to find drivers driving under the influence, the states that do have very strict guidelines on how to proceed.[xxv] In order for a check point to be utilized, every car must be stopped and searched by the same procedures.[xxvi] A police officer can run a background check on the driver to look for warrants and then verify that the driver’s license is valid and insurance is up to date.[xxvii] The police officer can then conduct tests, such as roadside test, to determine whether or not the driver is under the influence of drugs or alcohol – that would make them unsafe to drive.[xxviii]

dui checkpoint as one of the methods for dui detection in law enforcementA police officer cannot, however, force the driver to consent to a search of their car based solely off the check point stop.[xxix] The check point stop has limits to what the police officer can do when the driver is stopped, and searching their car is not within the scope. The police office must still have valid grounds to search the car independent of the check point stop. If a police officer violates the state laws in place for conducting a proper check point stop, all the evidence gathered during that stop may not be used in court. For example, if the officer conducts a breathalyzer test, even if it comes back to show the driver was above the legal limit, if the check point search was conducting outside the bounds the office was required to stay within – that breathalyzer test may not be something the court will allow.


Driving under the influence of drugs or alcohol is dangerous is a variety of ways. First of all, it is dangerous for all drivers on the road when another driver is operating their vehicle under the influence. Next, it is dangerous for the driver’s future. All it takes is once instance of drinking and driving to end up with m

[i] See DUI and DWI Laws. NOLO Driving Laws. (Accessed May 6, 2016).

[ii] See Comparing State DUI Laws. FindLaw. (Accessed May 6, 2016).

[iii] See DUI & DWI in Arizona. Department of Motor Vehicle. (Accessed May 6, 2016).

[iv] Id.

[v] Id.

[vi] Id.

[vii] Id.

[viii] Id.

[ix] Id.

[x] See Probable Cause and DUIS: 5 Things to Know. NOLO Driving Laws. (Accessed May 6, 2016).

[xi] See DUIs: What are the Visual Cues? NOLO Driving Laws. (Accessed May 6, 2016).

[xii] See Field Sobriety Test. Find Law. (Accessed May 6, 2016).

[xiii] Id.

[xiv] Id.

[xv] Id.

[xvi] Id.

[xvii] Id.

[xviii] See Breathalyzer Calibration. Find Law. (Accessed May 6, 2016).

[xix] Id.

[xx] Id.

[xxi] Id.

[xxii] See DUI Blood Tests. Drunk Driver Defense. (Accessed May 6, 2016).

[xxiii] See What to do and how to beat a best test DUI case. Fight DUI Charges. (Accessed April 6, 2016).

[xxiv] Id.

[xxv] See Requirements for  DUI Checkpoint. Criminal Law Free Advice Legal. (Accessed April 6, 2016).

[xxvi] Id.

[xxvii] Id.

[xxviii] Id.

[xxix] Id.