California v. Carney
The issue of warrantless searches has most often come up in relation to searches of automobiles. The Supreme Court treats cars in a special category with regard to the Fourth Amendment, and has allowed law-enforcement officers greater latitude in searches of automobiles than for other types of personal property. Justifications for this view include the fact that a car can easily be moved, and that the expectation of privacy is lower when one is in one's car.
Opponents of warrantless searches hold that such searches constitute an unduly lax regard of the Fourth Amendment, which may lead to increased police power to search other types of property--including one's home.
Is this as it should be? On the one hand, smoking marijuana while driving a vehicle is clearly more dangerous than when one is sitting at home. On the other hand, the right of police officers to stop a car for perceived violations of the law does not in itself imply that the driver should expect a lesser degree of privacy. After all, police can also see evidence of a violation at one's home--e.g., watering one's grass on a day when such is restricted due to drought--and this does not give officers the right to search for evidence of other violations.