When you are pulled over under suspicion of a DUI it is not just a breathalyzer you will face. There are a number of tests that an officer may give you to help him determine whether or not you are driving impaired. These are known as Field Sobriety Tests. Here are some of them:
The One Leg Stand is a test that seeks to determine and individual's ability to maintain balance. Typically the officer will ask an individual to stand on one leg and count to 30.
The Walk and Turn test is one where the officer will ask you to walk heel to toe in a straight line, turn and come back. This helps to determine coordination, balance and the ability to follow directions.
Horizontal Gaze Nystagmus is a test where the officer asks you to follow and object, typically a pen, with your eyes. If you are under the influence your eyes will tend to "bounce back and forth more" while following the object.
If you failed any field sobriety tests they can be challenged. Either in the way they were administered or in the way you failed them. For example, you may have an issue with your shoes or a medical condition such as arthritis which keeps you from passing tests.