The Fourth Amendment is part of the Bill of Rights, was introduced in Congress in 1789. The Amendment protects citizens from unreasonable searches and seizures conducted by police and other government agents. Reflecting a serious concern of the founding generation, the Fourth Amendment remains extremely important today, especially in light of the pervasiveness of crime, the threat of terrorism, and the national war on drugs. The Fourth Amendment generates countless court cases, as so many persons convicted of crimes challenge the means by which evidence was obtained against them. And it continues to provide a basis for important pronouncements by the Supreme Court that dramatically affect how law enforcement officials perform their jobs. The Fourth Amendment provides protection for criminal defendants. Bars the government from conducting unreasonable searches and seizures of person, house, papers, and effects. A seizure occurs when law enforcement use force detain a person, causing the person reasonable belief that he is not free to leave. A search must be reasonable, must have a search warrant unless is an exception. A search can occur under varied circumstances, for example, emergency search (a search conducted by a police without a warrant, believing it necessary and has no time to obtain a warrant). Also, a search can occur under a Border Stop(Checkpoints for excluding illegal aliens and contraband)etc.Warrantless searches of homes are unconstitutional under the Fourth Amendment except in “exigent circumstances”.According to case Florida v. Jardines Miami-Dade police department received an unverified notice, which indicated that the house of Joelis Jardines was being used to grow marijuana. A month later two detectives, together with a dog trained to detect drugs approached the residence. The dog handler accompanied the dog to the front door of the house, the dog signaled that it detected the smell of narcotics. The detective also smelled marijuana personally. The detective requested a search warrant which was issued. Jardines was arrested and charged with cannabis trafficking after a search confirmed that marijuana was being grown inside the house. Jardines argued that all subsequent evidence was the fruit of the poisonous tree and that the drug dog sniff was an impermissible search under the fourth amendment. The court of the first instance(Trial court) ruled to suppress the evidence. The State appealed the decision, concluding that the officer had the right to go to the door of the defendant and that this was not illegal, and for the dog to sniff it was not necessarily an order. With the delivered opinion 5-4 the court held that the front porch of a home is part of the home itself for fourth amendment purposes. To communicate with the occupants of the house, ordinary citizens are invited to enter by porch explicitly or implicitly. But the police officers cannot violate this invitation when conducting a search because a broader license is required and without this license, the police agents carried out an illegal search in violation of the fourth amendment. Judge Elena Kagan wrote an opinion in which she referred to privacy issues, as well as the property problems that the majority opinion addressed. People have a greater expectation of privacy in their homes and the areas surrounding their homes, and in this case, the police violated that expectation, because the cops used a dog that sniffs drugs.That was not used publicly to know details about the home, Judge Kagan argued that an illegal search had been carried out.The appellant stands convicted of knowingly having had in her possession and under her control certain lewd and lascivious books. According to the case, Mapp v. Ohio Mapp’s house was searched by three police officers who suspected that Mapp was hiding explosives in the residence, Mapp denied them the entrance if they did not present a search warrant. The officers left the residence but a few hours later they returned with the which was allegedly a search warrant. At that moment Mapp could not open the door, the officers violently entered the house. The petitioner asked about the search warrant the officers showed her and she took it and put it in her shirt pocket but then the officers recovered it. The officers carried out a generalized search of the residence and the petitioner was found guilty after officers found obscene materials in the basement.The petitioner was tried and convicted for these materials.Police may use such dogs at routine traffic stops or in airports without the need for a warrant or probable cause. In the court case, Illinois v. Caballes A drug-sniffing dog alerted the police about marijuana in the trunk of Roy Caballes’ car During a routine traffic stop.Caballes appealed that the search violated his Fourth Amendment right not to have to search or unreasonable confiscations, but the court upheld the conviction. The court mentioned that the rights of the fourth amendment were not violated because it is not necessary to have a reasonable suspicion for using drug-sniffing dog during a legal traffic stop because the dog only warns about the smell of marijuana. Caballes was convicted by an Illinois court for cannabis trafficking. The controversy over the exclusionary rule is far from over. It remains to be seen whether the court will extend the good-faith exception to warrantless searches involving unintended violations of constitutionally protected privacy.It is important to note, however, that a number of state supreme courts have refused to follow the good-faith exception with respect to the interpretation of their own state constitutional protections against unlawful search and seizure. One alternative to the exclusionary rule is filing a civil suit for damages against the officers who performed the illegal search. This remedy is especially appealing to persons who are victims of illegal searches or seizures but are not prosecuted for any crime. The exclusionary rule has generally been interpreted to dictate that evidence obtained by law enforcement in violation of the constitution usually cannot be presented during a criminal trial.The Validity of a warrant is based on four factors: whether the warrant is issued by a neutral and detached judicial authority,whether the warrant was based on a finding of probable cause(Use an affidavit),whether the warrant provides sufficiently detailed or particular instructions about the person or places to be searched and items to be seize,must be sufficiently precise in the warrant so as to avoid a general or overreaching search by the executing officer and whether the warrant was properly execute,must be executed by a public officer.Although the fourth amendment protects us from certain unreasonable searches, there are certain places where a search warrant is not necessary, for example at a border stop you do not need a search warrant but the stop must be between 100 air miles away. Also, a search warrant is not necessary when dealing with an emergency. The officer may need to act immediately and there is no time to obtain a search warrant. But an officer approaching the door of a house with the intention of obtaining evidence before obtaining the search warrant is unconstitutional because the officer obtained evidence illegally. This is known as “fruit of the poisonous tree” and the evidence can not be used in a trial.The court has held that the fourth amendment extends to any place or thing in which an individual has a reasonable expectation of privacy. Also, the fundamental requirement imposed by the fourth amendment is that searches and seizures must be reasonable. The amendment presupposes that searches will be authorized by warrants, and that warrants will not be issued without a probable cause.