Field sobriety tests assess coordination and cognitive function through physical performance tasks. Common tests include the horizontal gaze nystagmus (eye movement test), walk-and-turn test, and one-leg stand test. Officers score performance and use results as evidence of intoxication. However, these tests are highly subjective, influenced by medical conditions, anxiety, fatigue, and improper administration. Environmental factors like weather, road conditions, and lighting affect performance. Defense attorneys routinely challenge field sobriety test reliability and administration accuracy. Medical conditions including inner ear disorders, arthritis, and neurological issues cause poor performance independent of intoxication. Improper officer training, inadequate instruction, and scoring errors undermine test validity. Expert testimony often shows that test performance doesn’t reliably indicate intoxication. Courts increasingly recognize field sobriety test limitations.