There are a number of possible defenses against a DUI charge. Along with challenges to breath test results, you might also find that the officer who pulled you over did not have a proper basis to stop you in the first place. It may come as a surprise, but the police do not have the power to pull you over for just any reason.
A legitimate basis for a police officer to direct you to stop happens when a officer has a reasonable suspicion that you are driving while under the influence. Reasonable suspicion can take many forms.
Reasonable suspicion because of driving behavior
As FindLaw explains, officers might observe erratic driving behaviors that could indicate a driver has ingested too much alcohol. An officer might have reasonable suspicion to pull you over if you broke a traffic law while driving, like making an illegal turn, or if you took actions that made no discernible sense, like stopping in a lane, driving slowly, or braking when you have no reason to.
An officer might also claim reasonable suspicion after stopping you for reasons not related to a possible DUI. If you have a brake light out or an expired brake tag, an officer might pull you over for those reasons, and then later become suspicious that you may be under the influence after observing your behavior.
Reasonable suspicion for other reasons
An officer does not need to see you drive to suspect you are under the influence. Sometimes other circumstances may lead to a DUI stop and a possible arrest. For instance, a police officer might see a motorist unconscious in a parked vehicle or arrive at the scene of an automobile accident and decide to administer a sobriety test to the drivers involved.
Reasonable suspicion is not probable cause
While an officer may have reasonable suspicion to pull you over, it does not mean the officer can automatically arrest you. Reasonable suspicion only allows the officer to investigate for signs of a possible crime. So without strong enough evidence to lead an officer to think that you had likely committed a crime, such as the results of a breath test, the officer is unlikely to have the constitutional authorization to arrest you.