What is the test for determining whether a search or seizure under the Fourth Amendment is "unreasonable"?

The Fourth Amendment proscribes only "unreasonable" searches and seizures. However, the reasonableness of a search or a seizure depends "not only on when it is made, but also on how it is carried out." Tennessee v. Garner, 471 U.S. 1, 7-8, 105 S.Ct. 1694, 1699, 85 L.Ed.2d 1 (1985) (emphasis in original). In other words, even when supported by probable cause, a search or seizure may be invalid if carried out in an unreasonable fashion. We review a district court's determination of reasonableness de novo. See United States v. McConney, 728 F.2d 1195 (9th Cir.), cert. denied, 469 U.S. 824, 105 S.Ct. 101, 83 L.Ed.2d 46 (1984).