If you are driving under the influence of alcohol and are stopped by a police officer, you may be arrested. The first step of any criminal process is to place a person under arrest. The use of handcuffs as restraints is not required to place a person under arrest, and you are considered to be under arrest as soon as the officer says so, even if you aren't in custody.
Police officers cannot arrest you for no reason. The officer must have personally observed the crime, have probable cause, have an arrest warrant or be making a lawful traffic stop at the time when the DUI is suspected. If you are stopped without probable cause, then you are able to challenge the arrest as unlawful. For example, if you are driving safely when a police officer pulls you over and doesn't tell you why, you may be able to claim that the officer had no reason to stop you. Your attorney could use this information to help you get your case dropped.
If the officer stops you illegally, then any information he or she gathers from the stop cannot be entered into evidence. When your rights are violated, you have a chance to challenge the arrest and the actions of the police officer who arrested you.
An officer may not search your vehicle without probable cause or a search warrant. If you are stopped for speeding, for example, there is no reason for the officer to immediately ask you to open the trunk of your vehicle. If the officer orders you to open the trunk despite your reservations and a lack of probable cause to support the request, then you should tell this to your attorney who can help you challenge any evidence that was collected illegally.
Source: FindLaw, "DUI Arrest," accessed Oct. 26, 2016