No, that is not the case at all. I speak of "Probable Cause". When an officer has probable cause to believe a vehicle contains evidence or contraband, the officer may conduct a "warrantless" search of the vehicle. The only limits on this type of search would be based upon the object sought i.e. cannot look in the glove box for a stolen 27" television, or the information itself, i.e. officers information is that the item is in a particular place in the vehicle. Not required to make independent showing of exigency.
When police have reason to suspect that a vehicle contains a danerous item, which, if left unattended, endangers public safety, they may search the vehicle and remove the danerous item for safekeeping.
When an officer has reasonable suspicion to believe that a lawfully stopped vehicle contains a weapon, the officer may conduct a limited search of the passenger compartment (limited to those areas and items capable of containing a weapon).
In terms of home searchs there are a few warrantless searches that apply. The first being "Plain View". While lawfully present in an area protected by the 4th Amendment, the officer observes an item which he or she has probable cause to immediately believe is evidence or contraband, without making a further intrusion i.e. items on a bookshelf or on a cabinets that are in plain view. If the officer has to move an item, even slightly, to determine that it is evidence or contraband, the seizure is not valid under the plain view doctrine.
When officers make a valid arrest in a home the officers may, at the time of the arrest, conduct a search incident to arrest limited by the following rules:
Officers may thoroughly search the room where the arrest has taken place including areas capable of holding evidence or weapons. Officers need not articulate any suspicion that weapons or evidence exists, the arrest itself justifies the search.
Officers may look into (not go into) areas from which an attack could be launched adjoining the room where the arrest has been made. This look, does not require any suspicion that someone is about to attack but is limited to areas in which an attacker could be hiding.
Where officers can articulate reasonable suspicion to believe that an associate of the arrested person or some other third party is in the home and poses a danager to the officers; officers may do a limited protected sweep of the entire residence to ensure their safety. This protective sweep is limited to a viewing of areas where an attacker could be hiding. Items which are found during the protective sweep which meet the requirements of plain view may also be seized and used as evidence.
I hope this helps to clear the confusion.