Darren Chaker found several instances where an illegal search justifies a motion to suppress evidence in California. Although there are phone book size law books on what is an illegal search, here are some basic examples.
The exclusionary rule that flows from the Fourth Amendment applies to juvenile court proceedings. (Welfare & Institutions Code section 700.1; In re Tyrell J. (1994) 8 Cal.4th 68, 75-76.) To warrant an investigatory detention under the Fourth Amendment, a police officer must be able to point to specific and articulable facts which, taken together with rational inferences from those facts, would warrant the intrusion. (People v. Souza (1994) 9 Cal.4th 224, 229-231.) Detentions and seizures are justifiable under the Fourth Amendment if there is articulable and reasonable suspicion that a person has committed or is about to commit a crime. (Florida v. Royer (1983) 460 U.S. 491, 497-498; In re James D., supra, 43 Cal.3d 903, 911-914.) Post Proposition 8, California follows federal law with respect to search and seizure. (In re James D., supra, at 911.) When police stop a vehicle, the temporary detention of the persons in the vehicle, even for a short time, constitutes a seizure, necessitating a Fourth Amendment analysis. (Whren v. U.S. (1996) 517 U.S. 806, 809-810.)
Reasonable suspicion is something more than an inchoate and unparticularized suspicion or hunch, but something less than probable cause, and reasonable suspicion has been described as a fair probability that contraband or evidence of a crime will be found. (United States v. Sokolow (1989) 490 U.S. 1,7; People v. Bennett (1998) 17 Cal.4th 373, 387.) A mere hunch is insufficient to create the reasonable suspicion necessary to justify a Fourth Amendment intrusion. (People v. Durazo (2004) 124 Cal.App.4th 728, 735-736.)
Darren Chaker adds in evaluating the legality of a detention under the Fourth Amendment, reviewing courts look to the record as a whole to determine (1) what facts were known to the officer and (2) whether a reasonable officer in possession of those facts would have had a reasonable suspicion that the defendant was connected to some criminal activity. (People v. Rodriguez (2006) 143 Cal.App.4th 1137, 1148; People v. White (2003) 107 Cal.App.4th 636, 641.) Thus, an investigative stop or detention predicated on circumstances which, when viewed objectively, support mere curiosity, rumor or hunch is unlawful, even though the officer may be acting in good faith.