Police officers need a justification to demand a chemical breath test unless you willingly submit to the testing. If you caused a collision, that can be justification for testing. Otherwise, they require probable cause.
If you admit to drinking when you talk to them or show signs of impairment at the wheel, they may ask you to exit the vehicle to perform field sobriety tests. The results of those tests will determine if the officer can require you to perform a breath test next. What happens during a field sobriety test?
An officer looks for indications of alcohol intoxication
There are dozens of possible tests that a police officer can use, but there are three field sobriety tests considered to be the standard. One is the walk-and-turn test. The officer asks someone to walk in a straight line and then turn 180° and follow the same line back.
Another standardized test is the one-leg-stand test. Officers sometimes require that an individual balance and possibly answer questions or perform basic logic problems while standing on one leg. Finally, there is the horizontal gaze nystagmus, a test that looks for an enhanced muscle spasm when you move your eyes from side to side.
If a driver fails these tests, an officer will have an easier time insisting that they perform a chemical breath test and arresting them if they refuse. Of course, such testing is far from infallible, and you may still be able to challenge the results if you end up facing charges. Learning about how the state builds a case for drunk driving charges can help those recently arrested after a traffic stop.