According to Illinois v. Caballes, what restriction applies to traffic stops when using canine units?

The ruling in Illinois v. Caballes establishes that during a lawful traffic stop, the duration of the stop should not be extended unnecessarily for the purpose of conducting a canine search. In this case, the United States Supreme Court held that the use of a drug-sniffing dog does not violate the Fourth Amendment if it does not prolong the stop beyond the time necessary to address the violation that justified the stop in the first place. Therefore, the principle derived from this case emphasizes that while officers may utilize canine units, the stop should remain focused on its original purpose without unnecessary delays for the arrival or use of such units. This upholds the need to balance effective law enforcement with the protections against unreasonable searches and seizures.