Field Sobriety Tests: Are They Legally Required or Optional?
If you’re pulled over by a police officer who suspects you of driving under the influence, you may be asked to perform a field sobriety test.
Most people understandably feel nervous in this situation, unsure of their rights or the potential consequences of refusing. The truth is that field sobriety tests aren’t always what they seem—and understanding your legal obligations can make a major difference in your case.
As a Kansas City DWI attorney at Howard L Lotven, PC, I’ve helped countless individuals understand these challenging moments. Missouri law gives officers discretion in how they investigate suspected impairment, but drivers also have important rights.
Knowing when a test is required and when you can refuse can protect you from making costly mistakes. Contact me when you need to determine the difference.
What Are Field Sobriety Tests?
Field sobriety tests (FSTs) are physical and cognitive exercises that officers use during traffic stops to gauge a driver’s level of impairment. The goal is to help law enforcement determine whether probable cause exists for an arrest.
Common standardized tests include:
Horizontal Gaze Nystagmus (HGN): The officer tracks the driver’s eye movement as they follow a small object side to side.
Walk-and-Turn Test: The driver walks a straight line, heel to toe, then turns and returns the same way.
One-Leg Stand Test: The driver stands on one leg for a set time while counting aloud.
These tests were developed by the National Highway Traffic Safety Administration (NHTSA) to detect impairment, but they aren’t foolproof. Many people “fail” them for reasons unrelated to alcohol or drug use.
Are Field Sobriety Tests Mandatory in Missouri?
Unlike breath or blood tests, field sobriety tests aren’t legally required under Missouri law. Drivers have the right to politely refuse to participate.
However, many officers don’t make this clear during a stop. They might ask in a way that sounds like an order, leading drivers to comply out of fear or confusion. As a DWI attorney, I always advise clients to remember that cooperation doesn’t mean surrendering your rights.
Refusing a field sobriety test can’t directly result in a license suspension. However, it may still influence an officer’s decision to arrest.
How Officers Use Field Sobriety Tests
Officers use FSTs to gather evidence of impairment before making an arrest. They observe the driver’s balance, coordination, speech, and ability to follow instructions.
Yet these observations are subjective. Factors like nervousness, fatigue, uneven pavement, poor lighting, or medical conditions can all cause someone to “fail” even if they’re sober. Officers often record the test, and prosecutors later use that video in court as supposed proof of intoxication.
I’ve seen many cases where the results were misinterpreted or exaggerated. That’s why it’s essential to have a DWI attorney who understands how to challenge this type of evidence.
Why Officers Rely on These Tests Despite Their Flaws
Field sobriety tests remain popular among law enforcement because they help justify arrests and gather evidence for court. Even though the tests are subjective, officers often view them as a way to strengthen their case.
However, prosecutors still must prove guilt beyond a reasonable doubt. When a DWI attorney exposes inconsistencies in the officer’s observations or the conditions of the test, juries often question whether the results truly indicate impairment.
This is why it’s critical to have an attorney review every detail of the stop, from the officer’s initial contact to the final arrest decision.
What Happens If You Refuse a Test?
If you choose to decline field sobriety tests, the officer may still arrest you based on other observations—such as the smell of alcohol, slurred speech, or erratic driving. However, refusing can limit the amount of evidence available to the prosecution later.
Without video or notes from the tests, prosecutors have less material to use against you. As a DWI attorney, I often see cases where refusal made it more difficult for the state to prove impairment beyond a reasonable doubt.
Still, it’s important to remain polite and cooperative. Calmly saying, “I prefer not to perform any field tests,” is better than arguing or appearing confrontational.
How Field Sobriety Tests Are Scored
Each standardized field sobriety test has specific “clues” that officers look for to determine possible impairment. For example:
Horizontal Gaze Nystagmus: Involuntary eye jerking when tracking side to side.
Walk-and-Turn: Difficulty maintaining balance, improper turns, or missing heel-to-toe steps.
One-Leg Stand: Swaying, putting foot down, or using arms for balance.
Failing even a few clues can lead officers to conclude impairment. But these results are far from reliable. Studies have shown that fatigue, anxiety, poor footwear, or even being over 40 years old can cause people to “fail.”
In court, a skilled DWI attorney can question the officer’s training, the conditions of the test, and whether standardized procedures were followed correctly.
The Difference Between Field Sobriety Tests and Chemical Tests
It’s important to distinguish between field sobriety tests and chemical tests.
Field sobriety tests: Voluntary, subjective, and performed before arrest.
Chemical tests (breath, blood, urine): Administered after arrest under Missouri’s “implied consent” law.
Under implied consent, drivers who refuse post-arrest chemical tests can face automatic license suspension. Field sobriety tests, on the other hand, carry no such automatic penalty for refusal.
That distinction is critical. Many people mistakenly believe that refusing field tests will automatically cost them their license, but that only applies to chemical testing after arrest.
Nonstandard Field Sobriety Tests
Some officers use “nonstandard” tests that aren’t approved by the NHTSA, such as asking the driver to recite the alphabet, touch their nose, or count backward. These are even less reliable and can easily be challenged.
If you were arrested after performing one of these unapproved tests, your attorney can argue that the results should be excluded from evidence. Courts tend to give nonstandard tests little weight because they lack scientific validation.
Video Evidence and Officer Subjectivity
Body camera and dashcam footage have become increasingly important in DWI cases. While officers claim that field sobriety tests provide objective signs of impairment, videos often tell a different story.
In some cases, the footage shows the driver performing reasonably well or the officer giving confusing instructions. As a DWI attorney, I always request all available video evidence to review how the tests were conducted.
This type of evidence can reveal bias, mistakes, or inconsistencies in the officer’s testimony—key points that can help undermine the prosecution’s case.
Implied Consent in Missouri
After a DWI arrest, Missouri’s implied consent law requires drivers to submit to chemical testing. Refusal of a chemical test can lead to automatic license suspension and other penalties.
However, this law doesn’t apply to pre-arrest field sobriety tests. That means drivers retain the full right to decline FSTs without facing immediate administrative consequences.
This distinction is often misunderstood, and law enforcement officers may use confusion to their advantage. Knowing the difference before an encounter can help you make an informed decision.
Misconceptions About Refusing Field Sobriety Tests
Many people mistakenly believe that refusing a field sobriety test will automatically make them appear guilty. However, officers already suspect impairment when they ask for the test. Performing poorly can only make things worse.
Refusal may not stop an arrest, but it prevents the officer from collecting additional evidence. I often tell clients that politely declining is a lawful, strategic decision—not an admission of guilt.
As a DWI attorney, I’ve seen many cases dismissed or reduced because the prosecution lacked reliable field test results.
Protecting Your Rights During a DWI Stop
If you’re stopped by police in Missouri, remember these key principles:
Be polite and cooperative: Never argue or resist.
Provide identification: Hand over your license and registration when asked.
Exercise your rights: You don’t have to answer questions about drinking.
Refuse field sobriety tests: You aren’t legally required to perform them.
Request an attorney: Ask to speak with a DWI attorney immediately if you’re arrested.
Following these steps helps preserve your legal options and makes sure that your rights remain intact.
Reach Out Today
At Howard L Lotven, PC, I represent drivers throughout Kansas City, Missouri, and nearby communities, including Independence, Rock Port, and Lexington. Field sobriety tests can be intimidating, but they aren’t mandatory—and understanding your rights is essential.
As an experienced DWI attorney, I help clients challenge unreliable test results, protect their driving privileges, and fight for fair outcomes in every case. Contact me to get started with your case.