Undercover operations in which the agent is an invited informer, in what circumstances will the agent not be able to conduct a search under the Fourth Amendment?

Undercover operations, in which the agent is a so-called "invited informer," are not "searches" under the Fourth Amendment. Id. at 701 (citing Maryland v. Macon, 472 U.S. 463, 105 S.Ct. 2778, 86 L.Ed.2d 370 (1985)). Even though a conversation between an agent and a target may occur in an otherwise private environment, "a person has no legitimate expectation of privacy in information he voluntarily turns over to third parties." Id. at 698 (quoting Smith v. Maryland, 442 U.S. 735, 743-44, 99 S.Ct. 2577, 61 L.Ed.2d 220 (1979)). Finding an expectation of privacy in the defendants' surreptitiously recorded comments would have been, we observed, "inimical to established fourth amendment doctrine." Id. at 699.