When a police officer suspects that you have had too much to drink, they will try to find evidence so that they can arrest you. Unless you admit to over-consuming when they ask you questions, they will probably ask you to exit the vehicle and perform a field sobriety test. The way that you perform on that test will determine what happens next.
There are typically three standardized tests that officers expect you to perform during a traffic stop.
The walk-and-turn test
Alcohol effects your balance and spatial reasoning, so it can be difficult to walk in a straight line when you have had a couple of drinks. Having you walk in a straight line and then turn and walk back along the same line can allow an officer to spot warning signs that someone has a dangerous level of alcohol in their bloodstream.
The one leg stand test
Even if alcohol does affect your balance, you may be able to adjust for that by continuing to move during the walk-and-turn test. The one leg stand test highlights balance issues by forcing you to stand on one leg, possibly while answering questions or reciting the alphabet. If you cannot maintain your balance, that will make an offer more suspicious of possible chemical impairment.
The horizontal gaze nystagmus
There are numerous explanations for issues with balance or someone’s gate. The horizontal gaze nystagmus test is a test that is harder for someone to explain away if caused by secondary factors. A police officer orders you to follow their finger with your eyes without turning your head. There is a small muscle spasm that typically occurs when you complete side-to-side motions with your eyes, and that spasm will become much more noticeable after someone consumes alcohol.
The way that you perform on a field sobriety test can give an officer the probable cause that they need to request a chemical breath test from you. Understanding how police officers build a criminal case can help you defend against pending drunk driving charges.