Police officers watch for signs of impairment when they are out patrolling. If they see signs that someone is impaired, they are going to pull the vehicle over. Once they have the driver with them, they are going to try to figure out what's going on. They can do a field sobriety test and chemical testing to determine whether the person is under the influence of something that is affecting their ability to drive.
One thing that many people don't realize is that all sobriety tests aren't the same. Some tests are standardized while others aren't. The Standardized Field Sobriety Test is the only one that is endorsed by the National Highway Traffic and Safety Administration (NHTSA). There are three components of this test: the one-leg stand, the horizontal gaze nystagmus and the walk-and-turn. Together, these can provide a fairly accurate estimation of impairment.
When you put the results altogether for these tests, alcohol impairment is accurately indicated around 91 percent of the time. This leaves a full 9 percent of cases that might have incorrect results, so it might be possible to use this as a component of your defense.
Any other tests that are done at the roadside aren't part of the SFST battery. These include things like tipping your head backward or touching your nose with a finger while your eyes are closed. Tests that aren't part of the SFST haven't been proven effective in gauging impairment.
The large variety of things that might happen during a traffic stop for suspected drunk driving demands that anyone charged with this crime takes swift action. Ensure that you consider everything that happened during the stop, so you can use what you need in your defense.