When you roll down your window at a traffic stop, if the cop smells "the odor of intoxicating beverages" that can form the basis of a probable cause search. The fact that a dog has a more sensitive shouldn't change the law.
Would you then extend that to very sophisticated electronic monitoring systems? The trade-off, of course, is the more sensitive the monitoring system, the higher rate of false positives and thus the more harrassment of innocent citizens. Where do you draw that line?