In United States v. Colyer, 278 U.S. App. D.C. 367, 878 F.2d 469 (D.C. Cir. 1989), the Court of Appeals upheld the proposition that the canine "sniff of the exterior of an Amtrak roomette" was not a Fourth Amendment search. 878 F.2d at 473. The opinion stressed the limited and binary nature of the canine inquiry.
As in Place, the driving force behind Jacobsen was the recognition that because of the binary nature of the information disclosed by the sniff, no legitimately private information is revealed: That is, "the governmental conduct could reveal nothing about noncontraband items.
In our view, then, Place and Jacobsen stand for the proposition that a possessor of contraband can maintain no legitimate expectation that its presence will not be revealed. Stated otherwise, governmental conduct that can "reveal nothing about noncontraband items" interferes with no legitimate privacy expectation. (878 F.2d at 474.)