When a search and/or seizure is conducted without a warrant, what is the test for obtaining a search warrant?

When a search and/or seizure is conducted without a warrant, the key question is whether the warrantless conduct of the law enforcement officers invades a defendant's reasonable expectation of privacy; if so, the conduct impinges on the defendant's Fourth Amendment rights. (See, e.g., California v. Ciraolo (1986) 476 U.S. 207, 106 S.Ct. 1809, 90 L.Ed.2d 210 (overflight of backyard for observational purposes is not an invasion); Katz v. United States, supra, 389 U.S. at p. 353, 88 S.Ct. at p. 512 (electronic eavesdropping is an invasion and, in the absence of a warrant authorizing it or a recognized exception to the search warrant requirement, an unreasonable one). The Fourth Amendment, however, does not create privacy rights; it only protects certain of them against particular infringements. (Katz v. United States, supra, 389 U.S. 347, 88 S.Ct. 507.)