What Are Field Sobriety Tests (FSTs)?
Field Sobriety Tests (FSTs) are a series of physical and mental exercises that law enforcement officers ask drivers to perform during a DUI investigation.
Despite what many people believe, FSTs are not designed to determine whether you are safe to drive. They are not pass-fail tests meant to separate sober drivers from impaired ones. Their real purpose is to create probable cause so an officer can arrest you for DUI.
In Utah, FSTs commonly include:
- Horizontal Gaze Nystagmus (HGN) – The officer checks whether your eyes track smoothly or involuntarily jerk when moving side to side.
- 9-step walk and turn – You are asked to follow detailed instructions, walk heel-to-toe in a straight line, turn in a specific way, and return—without making mistakes or asking questions.
- One legged stand — You are instructed to stand on one leg, in a specific position, for a specific amount of time, exactly as directed.
Even completely sober people routinely struggle with these tests.
Do You Have to Do FSTs in Utah?
No. Utah law does not require drivers to submit to Field Sobriety Tests.
The Utah legislature has given police authority to require a chemical test (breath, blood, or urine) after there is probable cause for DUI. Refusing a chemical test can result in an 18-month license suspension.
That same authority does not exist for FSTs.
Why Police Ask You to Do FSTs
FSTs exist to help officers build probable cause. Before the tests, the officer may not yet have enough evidence to legally arrest you.
Without probable cause:
- You cannot be arrested
- You generally cannot continue to be detained
For this reason, experienced officers often skip FSTs entirely when they already believe someone is impaired. Obvious signs like:
- Smell of alcohol
- Bloodshot or watery eyes
- Slurred Speech
- Confusion or poor coordination
If an officer asks you to perform FSTs, it is usually because they want more evidence, not because they are undecided.
Treat FSTs Like Police Questioning
Field Sobriety Tests should be treated the same way as answering police questions or making statements:
Don’t do them.
They are voluntary, and they are designed to produce evidence against you.
What Will Happen if I Refuse?
If you refuse to perform FSTs, there is a good chance you will still be arrested for DUI. However, by the time the officer asks you to do the tests, the decision to arrest has often already been made.
Refusing simply prevents you from:
- Providing additional evidence
- Giving the officer video footage of you struggling with coordination
- Strengthening the case against you
A Critical Point Most People Miss
Most DUI arrests assume alcohol impairment and rely on chemical tests that measure alcohol concentration.
If you:
- Haven’t been drinking alcohol, but
- Perform poorly on FSTs
The police can still charge you wil DUI and argue you were impaired by another substance or drug.
By performing FSTs, you give them that opportunity—even if no alcohol is involved.
Conclusion
It should go without saying: don’t drink and drive. Use a designated driver or a rideshare service.
But if you are pulled over on suspicion of DUI—even if you are sober—do not answer questions and do not perform Field Sobriety Tests.
Even if you are arrested anyway, you will be in a much better position by not giving the police additional evidence to use against you.
