The Standard Field Sobriety Test actually consists of three separate tests that law enforcement officers may ask you to take if they believe you have been driving while under the influence of alcohol or drugs. Theoretically, if you fail one or more of these tests, officers have the probable cause they need to arrest you for DUI.
The problem with SFSTs, however, is that you may fail them even if you are “stone cold sober.” Why? Because numerous factors influence how well you perform on them.
Factors affecting outcomes
Factors that influence how well you perform on the SFSTs include the following:
- Your age
- Your weight
- Medical conditions from which you suffer
- Legal prescription drugs you take for these conditions
- How well the officer instructs you
- How well (s)he observes and interprets your performances
Horizontal gaze nystagmus test
The HGNT tests the way in which your eyes track an object. The officer holds a pen, small flashlight or some other small object in front of your face and instructs you to track its movement without moving your head. Then (s)he slowly waves the object back and forth horizontally in front of you. Theoretically, if inebriated or under the influence of illegal drugs, your eyes will “jump around” instead of smoothly moving back and forth.
The WATT tests how well you maintain your balance while walking. However, the officer does not test your normal gait. Instead, (s)he instructs you to walk heel-to-toe for nine steps, stop, turn around and walk back, again heel-to-toe. Theoretically, if inebriated or under the influence of illegal drugs, you will not be able to complete this test without losing your balance.
One-legged stand test
The OLST also tests your balance level. Here the officer instructs you to stand on one foot while keeping your other foot raised about 6 inches above the ground and your arms at your sides. (S)he will tell you to stand this way for at least 30 seconds. Theoretically, if inebriated or under the influence of illegal drugs, you will not be able to do this without putting your raised foot down or moving your arms to help you balance.