Unlocking the Mystery of DUI Field Sobriety Tests

car keys and shot glasses

A little bit of knowledge is a dangerous thing. The internet has lots of incorrect information about DUI sobriety testing. When the matter is serious as losing your license – or even jail time – you want advice from an expert.

I am that expert.

What makes me qualified to help you unlock the mysteries of DUI sobriety testing? I have…

…prosecuted hundreds of DUI’s as a Deputy County Attorney.
…cross examined endless law enforcement officers.…defended several hundred clients as a private defense attorney.
… tried DUI cases before several juries.
…been involved in DUI breath test litigation and legislation..…pored over police training manuals to know them inside and out.

It’s not illegal to have one drink and then drive. It is also not illegal to take a valid prescription and then drive. It is illegal to drive “impaired”. The tricky thing is that “impaired” doesn’t have a black and white definition. Law enforcement uses tests to gather evidence that an individual is driving impaired.

car keys and shot glasses

There are two types of impairment tests. There are physical Field Sobriety Tests, where you’re asked to perform a set of tasks. There are also machine measured alcohol concentration tests. These detect the amount of alcohol in your system using a blood, breath, or urine sample.

The first thing you need to understand is that you cannot “pass” a sobriety test. In the rare case that an officer believes you have not shown any indications of impairment, they may choose not to charge you with a DUI. Usually, though, the tests do show some signs of impairment.

That’s when you’ll want a defense attorney on your side. A good defense attorney will look over the video of you performing the tests and interview the officer that tested you. An experienced defense attorney can use this testing to your advantage. He or she can help you win your case or get a reduced charge.

You can help your case by understanding the field sobriety tests. Of course, nobody plans on driving impaired. But if you plan on going out on the town – even just for a beer or two – you should prepare for the worst. It is in your best interest to understand the field sobriety tests used in Montana. Knowing what you may be up against will help you perform better under pressure.Ready to get started?

The FST Basics

How do you decide that an individual is impaired? Law enforcement uses nationally recognized techniques of observing indications of alcohol or drug impairment. These tests compose what we call Field Sobriety Testing. This testing may take place where a law enforcement officer stops the subject, or in a detention center.

Several recognized tests exist. In Montana the majority of law enforcement agencies use four FST’s. They are the HGN test, the walk and turn test, the one-leg stand test, and blood alcohol level tests. Let’s look at these tests in more detail.

The HGN Test

HGN stands for ‘Horizontal Gaze Nystagmus’. For this test, officers have you keep your head straight and follow their finger or a pen with your eyes. The officer will start by holding the pen in front of your face. The pen is then slowly moved horizontally in front of your face to extreme angles to the sides of your face and held there. As your eye focuses on and follows the pen, the officer may or may not see the “jumping” or Nystagmus in your eye throughout the test.

Nystagmus or eyeball ‘jumping’ in the eyes can occur when a person is intoxicated. Typically the more instances of nystagmus a person exhibits, the more intoxicated they are.

The Walk and Turn Test

The Walk and Turn Test is also called a “Divided Attention” test. This test shows the officer several things. It shows him or her your ability to listen to and retain instructions, your balance, and your focus.

dui field test walking in a straight line

An inability to do any of these things is considered a sign of impairment.

First the officer will give you specific instructions in a certain order. If you can’t remember all the instructions in the correct order, the officer marks it as a sign of impairment.

The officer will instruct you to place one foot in front of the other, heel to toe. He or she will ask you to hold that position without breaking it, and without raising your arms or losing balance. (Take a second to stand up and try this. It’s not easy sober, either!) If you break that stance, the officer will note it as a sign of intoxication.

While you are holding that tricky position, the officer explains the balance part of the test. The officer will ask you to walk a straight line like a tightrope. You’re expected to place each foot in front of the other, touching them heel to toe, just like in the original stance. You will be asked to count out exactly 9 steps, and then use one foot to complete a 180 degree turn on the line.

Finally, the officer will ask you to do the same tightrope-style walk to the beginning of the same line.

During this balance test, the officer is looking for you to…

  • Take too few or too many steps
  • Break your stance before you begin the test
  • Complete the turn other than the exact way he showed you
  • Count the number of steps out loud
  • Lose your balance
  • Step off the line
  • Not touch heel to toe
  • Raise your arms

Doing any of these things, or otherwise breaking the officer’s initial instructions, is considered a sign of impairment.

Does this seem hard? It is. Whether you’re stone sober or three sheets to the wind, this is a difficult test to complete perfectly. There are so many aspects to getting it just right. When you’re under pressure, you’re not going to be able to execute it flawlessly. Almost no one can unless they are trained in the test.

You do have the right to refuse these tests, but if you perform them, do your best, and have a good attorney.

The One-Leg Stand Test

The final test that’s typically used by Montana Law Enforcement is the One-Leg Stand test.

The officer will have you stand with your feet next to each other and arms by your side. The officer will ask to stand this way while they give instructions and show you an example of what the test looks like.

This test consists of standing on one foot and raising the other foot approximately 6 inches off the ground. As you hold your foot extended in front of you, you want to point your toe forward and keep your eyes on the raised toe. Then, you’ll audibly count from one to thirty before putting your foot down again.

As you perform this test, the officer is looking for several things. They’re looking to make sure that you are able to listen to instructions and hold your balance. They check to see that you raise your foot the correct distance off the ground, and that you can count to thirty in the correct order.

Any of the following behaviors count as signs of intoxication:

  • Deviating from instructions
  • Counting unintelligibly or out of order
  • Not being able to concentrate on instructions
  • Lifting your foot to high or not raising it high enough
  • Dropping your foot before you finish counting to thirty
  • Not looking at your foot
  • Hopping on one foot to maintain balance
  • Not being able to maintain your balance
  • Raising your arms to maintain balance

Again, this test is difficult under even the best circumstances.

The Blood Alcohol Tests

After you’ve completed the field sobriety tests, the officer will almost always request a breath test. Thankfully, you will no longer have to perform any physical stunts. The officer will simply ask you to breath into a machine.

The Portable Breath Test (PBT) is about the size of a small juicebox. It has a little white tube at the top. The officer will ask you to breath into the tube to get a reading of your blood alcohol content.

In Montana, an individual with a reading from .000 – .04 is considered not impaired (if you are over 21 years of age). An individual with a reading from .04 – .08 may be considered impaired. This means that the officer may arrest you for a DUI based on the other testing and their evaluation of you and your driving behavior. Finally, an individual with a reading above .08 is presumed to be impaired.

crunched front bumper due to dui

This is where a lot of people stumble in the testing process. Evaluating your performance in field testing is subjective, making it relatively easy to debate in court. The numerical results of a breath test are difficult to challenge in court. If you consumed more than 1 drink per hour before getting into your car, you would be wise to consider refusing a breath test.

If you refuse the breath test (or cannot complete it for whatever reason), an officer may request a blood test. You may refuse this type of testing as well, but in Montana an officer can in some cases request a search warrant to force you to comply to a blood test. This law is somewhat new, and is regularly challenged in courts. A medical professional will draw your blood and the State Crime Lab will test it. The results of this test is considered more concrete evidence of intoxication than the breath test.


As you can see, there are many things a law enforcement officer must take into consideration when determining if there is enough evidence to support a DUI charge. You have the right to refuse to do any of these tests, but an officer is unlikely to tell you that. The best way to reduce your charge or avoid one all together is to find a good defense attorney. The defense attorney can look over the video of you performing the field tests, and interview the officer to determine whether testing was done correctly. Improperly calibrating machinery for the breath test can also help you win your case or get a reduced charge.

But it takes an experienced defense attorney to know what to ask.

What you’ve just read is a summary of what I have learned about sobriety testing. I base this knowledge on my over 12 years of experience dealing with DUIs in Montana.

Did I leave anything out? I don’t think so. But if you have any questions, leave a comment. I’ll either answer your concerns in a comment or write a separate post addressing your question.