What are DUI Field Sobriety Tests? (Or, the Emperor has no Clothes, DUI Edition)

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What are field sobriety tests and how are they used by the police in DUI stops?

Are they reliable? Or, is it like The Emperor has no Clothes, and everyone pretends as if it works because it’s the best we’ve got?

In this blog post, we are going to review the basics of how field sobriety tests work (and don’t work) in SC, including:

  • Standardized field sobriety tests (SFSTs),
  • Non-standardized field sobriety tests, and
  • Why FSTs are not a reliable indicator of a person’s intoxication level.

Standardized DUI Field Sobriety Tests in SC

There are just three field sobriety tests that have been approved by NHTSA for use in DUI detection.

Although none of the FSTs are reliable indicators of a person’s blood alcohol content (BAC), for reasons I will explain below, NHTSA has acknowledged that the only “tests” that are supported by scientific evidence are:

  • The horizontal gaze nystagmus (HGN) test,
  • The walk and turn test, and
  • The one-legged stand test.

Horizontal Gaze Nystagmus (HGN)

Nystagmus is a medical condition that causes an involuntary jerking of the eye, sometimes only when the eye is looking to one side or the other, but also sometimes when the eye is resting and looking straight ahead.

To perform the test, the officer will move a small light or pen back and forth in front of the subject’s eyes (following strict instructions from the officer’s training manual) and look for one or more “clues” that will allow the officer to say the subject has “failed” the test, including:

  • Whether both pupils are equal size,
  • Whether the eye shows nystagmus at maximum deviation (to the sides) or resting nystagmus, and
  • Whether the eyes “track” smoothly from side to side.

Nystagmus could indicate that a person is intoxicated. It is an unreliable test, however, because nystagmus could just as easily indicate that a person has one of many medical conditions that cause nystagmus

The SC Supreme Court has held (in State v. Sullivan) that the HGN test is not sufficiently reliable to be admitted as evidence in court unless it is offered in conjunction with the other field sobriety tests.

Walk and Turn Test

Stand with your feet one in front of the other, heel to toe, with your arms at your side, and hold this position until I finish giving you the instructions.

Let’s stop right there. Try it. Hold the position without moving for a while. If you managed to do it, now imagine you are overweight. Or you have poor balance. Or you have had an injury at some point to your leg or foot. Or you just stepped out of your car after driving for a few hours and your whole body is cramped up.

If you lift your arms, move your feet, sway while standing there, or start walking before the officer says go, these may be clues that the officer will use to say that you “failed” the test…

Take nine heel-to-toe steps along this imaginary line as I am demonstrating for you, when you get to the end, turn around but do it exactly as I am demonstrating for you, and then take nine heel-to-toe steps back to this spot.

If you lose your balance while walking and (unnaturally) touching your heel to your other foot’s toe with each step, lift your arms, step off the line, forget the exact method for making your turn at the end, take the wrong number of steps, or begin before the officer says, “go,” these may be clues that the officer will use to say you “failed” the test.

One-Legged Stand Test

Stand right here, with your feet together, arms at your sides, and do not move until I finish giving you the instructions.

Even before the test begins, if you shuffle to keep your balance, lift your arms, or lift your foot before the officer says, “go,” these are clues that the officer may use to say that you “failed” the test.

Raise one leg with your foot exactly six inches from the ground, with your foot parallel to the ground, with your legs straight, with your arms by your sides, and count “One one thousand, two one thousand” until I tell you to stop counting.

If you don’t keep your foot parallel to the ground, start before the officer says “go,” sway while you are standing there with your feet together, lift your arms to keep your balance, or stop counting at 30 when the officer didn’t say “stop counting now,” these may be clues that the officer will use to say that you “failed” the test.

Non-Standardized Field Sobriety Tests

There is a long list of field sobriety tests that police have used in the past (and sometimes still use) that even NHTSA has said are unreliable and have no scientific basis, including:

  • Holding your head back with your eyes closed and touching your nose with your index finger,
  • “Alphabet tests” where you must say the alphabet starting and ending with a specific letter or even backward,
  • Touching each finger with your thumb as you count, sometimes starting and ending with a specific number, or
  • Patting one hand with the other hand, then alternating the top/bottom hands as you count.

Are Field Sobriety Tests a Reliable Indicator of BAC?

Even the three standardized field sobriety tests are not a reliable indicator of BAC, despite NHTSA’s studies claiming that the tests are 91% effective if used in conjunction with each other.


  1. The FSTs are subjective and based on the officer’s observations (and bias),
  2. The FSTs are as likely to indicate a person has health problems or medical issues that affect balance as they are to indicate that a person is intoxicated, and
  3. The FSTs do not tell an officer how much a person has had to drink – they do not judge a person’s BAC at all.

FSTs are Subjective

Field sobriety tests are designed for you to fail.

If the officer thinks that you are DUI, he or she will find enough “clues” on the three tests to say that you “failed” the test. Test it yourself – if you administer these tests to anyone – stone-cold sober – you too will be able to find enough “clues” to say that they “failed” the test.

If the officer thinks that you are DUI, you will “fail” the FSTs. And, if the officer doesn’t think that you are DUI, they wouldn’t be giving you the test, would they?

DUI Defense Lawyers in Columbia, SC, and Myrtle Beach, SC

The Myrtle Beach and Columbia, SC criminal defense lawyers at the Thompson & Hiller Defense Firm focus exclusively on criminal defense cases in SC, including driving under the influence charges. We have obtained dismissals, pre-trial diversion resulting in dismissals, or acquittals following trial in hundreds of criminal cases, and we have a record of proven results.

If you have been charged with a crime in SC or if you think you may be under investigation, call us now at 843-444-6122 or contact us through our website for a free initial consultation to find out if we can help.