The three field sobriety tests that are commonly used by law enforcement officers to identify suspected drunk drivers are:

1. Horizontal Gaze Nystagmus (HGN) Test: This test involves the officer moving an object before the suspects eyes to determine the degree to which the suspects eyes can smoothly follow the object, to assess jerkiness of the eyes when held at maximum side deviation, and to determine the point at which eye jerking begins.

2. Walk-and-Turn Test: This test involves nine heel-to-toe steps along a straight line, turn on the line, and a nine-step return. The test gauges the suspects ability to perform a simple physical task and follow verbal instructions.

3. One-Leg Stand Test: This test involves the suspect standing on one leg while counting aloud. The test measures the suspects ability to balance, listen to instructions, and count aloud.

These tests are designed to measure specific responses or reflexes that some researchers believe are compromised if a person has been drinking. The National Highway Traffic Safety Administration (NHTSA) has sanctioned these three field sobriety tests, and they should be used in combination to ensure maximum accuracy in determining probable cause for a drunk driving arrest.