Which of the following tests is commonly used as part of the SFST battery?

The Horizontal Gaze Nystagmus (HGN) test is widely recognized as a crucial component of the Standardized Field Sobriety Tests (SFST). It involves observing the eyes of a subject as they follow a moving object, typically a pen or flashlight. The test measures the involuntary jerking of the eyes, known as nystagmus, which can become more pronounced under the influence of alcohol.

This test is based on the premise that alcohol can impair the brain's control over eye movement, and the presence of nystagmus can be a strong indicator of intoxication. The HGN test is scientifically validated and is considered reliable in assessing a driver’s level of impairment. Its inclusion in the SFST battery is due to its effectiveness in detecting impairments that are commonly associated with alcohol consumption, making it a critical tool for law enforcement officers in DUI investigations.