Scientific research now establishes that drug-detection dogs do not alert to the contraband itself. Instead, drug-detection dogs alert to certain volatile substances – generally, break-down products of the illegal drug. These decomposition odor constituents are in no way illegal or even unique to contraband. In fact, these volatile molecules or compounds are also found in substantial quantities in ordinary household items. Therefore, rather than detecting the contraband itself, a detection dog's alert to these entirely legal molecules or compounds instead produces an inference that contraband is also present. Because the canine-sniff technique relies on detection of noncontraband molecules and compounds within a home as the basis to infer that contraband is hidden inside, a canine drug-detection sniff is "capable of detecting lawful activity" within the home. Scientific research establishes that instead of smelling cocaine, drug-detection dogs alert to methyl benzoate – an odor shared by snapdragons, petunias, perfumes and food additives. Instead of smelling heroin, drug-detection dogs alert to acetic acid – an odor shared by vinegar and aspirin that is past its prime. Instead of smelling MDMA ("Ecstasy"), drug-detection dogs alert to piperonal – an odor shared by soap, perfume, food additives and even lice repellant. (citation omitted)

— Brief of amici curiae Fourth Amendment Scholars in support of respondent[36]