Generally speaking, can law enforcement authorities use nuclear detection devices against someone’s house without a warrant? This question is at root of the latest “no warrant” controversy. Readers would do well to examine the Supreme Court case Illinois v. Caballes, decided earlier this year. The Court ruled that when a dog sniffed out drugs during a routine traffic stop, without a warrant, it did not constitute an illegal search because, in the words of Justice Stevens, “Official conduct that does not ‘compromise any legitimate interest in privacy’ is not a search subject to the Fourth Amendment. Jacobsen, 466 U.S., at 123. “The Court noted that “any interest in possessing contraband cannot be deemed ‘legitimate,’ and thus, governmental conduct that only reveals the possession of contraband ‘compromises no legitimate privacy interest.’ Ibid.” Note that in an earlier case, Kyllo v. US, the Court ruled that thermal detection devices could not be used to surveil houses without a warrant because this would compromise privacy — the difference being that such devices pick up licit as well as illicit activity. In his dissent in that case, Justice Stevens pondered whether “public officials should not have to avert their senses or their equipment from detecting emissions in the public domain such as …radioactive emissions .. which could identify hazards to the community. In my judgment, monitoring such emissions with ’sense-enhancing technology,’ … and drawing useful conclusions from such monitoring, is an entirely reasonable public service.” Clearly Caballes rather than Kyllo controls in the case of using detection equipment to pick up emissions from nuclear materials banned under 18 USC 831 since, to quote Stevens’ majority opinion, such activity “reveals no information other than the location of a substance that no individual has any right to possess.” And even if you want to subject this to a balancing test, I think the government would not have to argue very strongly that there is a compelling state interest in keeping nuclear weapons out of the hands of private citizens.