The area around a person's home, in legal terms, is called the curtilage. This area is constitutionally protected from warrantless search and seizure. For example, a police officer would generally need a warrant to enter and search your yard, your private garage or another area around your home where you have a reasonable expectation of privacy.
What gives a police officer the right to stop your vehicle? Basically, the officer must have reason to suspect that a violation has been committed, but what constitutes reasonable suspicion is not always clear.