One exception to the fourth amendment that requires a search warrant can be a vehicular search. Vehicular searches allows for a person's vehicle to be searched without a search warrant if the officer undertaking the search has probable cause to believe that the vechicle obtained contains contraband. Your privacy in a residence is higher than it would be in your car. Privacy is lowered in your vehicle because it is a mobile environment where you encounter other drivers and predistrication. To maintain the safety of yourself and others on the road vehicle searches done by police officers without a search warrant are legal and needed in order to limit the potential danger in the environment.
An example
An example