A “warrant” is a broad term for some form of judicial authorization to search a place or person. In the case of DUI litigation, it usually refers to either a “search warrant” or a “blood warrant.”
In both cases, the police are required to get an “Information to Obtain,” which is essentially a form of affidavit. These “ITOs” can be challenged on both constitutional (Charter) and statutory grounds.
While most DUI files do not involve warrants, so do, and these are usually the more serious ones. Warrants are much more common when there has been a motor vehicle accident and/or an injury or death.
Like most areas of impaired driving, this is a very technical area of the law and the defence can be quite counter-intuitive.