Evidence or belief that a drug for example is inside the house, or no warrant is needed by police in some cases if the police belief that a person is hiding in the home.

Added; All that is needed is "Probable Cause to Believe" that items/person/etc is within a certain location - as spelled out in the affidavit which is presented to a judge for signature.

The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.

No unreasonable searches can be made unless they have a warrant or a written statement saying they can do the search in the house

The fourth amendment of the Constitution is part of the Bill of Rights and basically guards against unreasonable searches and seizures. It's the reason people on like CSI can't go inside someone's house or search their car without a warrant. Unless the police have probable cause against you, they cannot search or arrest you without a warrant.
The amendment specifically requires search and arrest warrants be judicially sanctioned and supported by probably cause. It was adopted as a response to the abuse of the writ of assistance, which is a type of general search warrant, in the American revolution. Search and arrest should be limited in scope according to specific information supplied to the issuing court, usually by a law enforcement officer, who has sworn by it.
Protects Americans "against unreasonable searches and seizures"
The fouth amendement states that we the citizens should protect individuals against unreasanble searches and seizures
The fourth amendment protects citizens from unreasonable searches and seizures (a legal procedure where, if the police or other authorities suspect a crime has been committed, they can search a person's property to get evidence). In addition, it also requires search and arrest warrants to be judicially sanctioned and supported by probable cause (the standard by which officers have the grounds to arrest someone).
George Washington
The 4th Amendment was important back then, because the British had the right to invade colonists homes and seize and/or charge the person with crime. The founding fathers wanted to protect the citizens in the future. This is important now because people can go on with their daily lives w/o the fear of government interfering. (:

I'll assume you meant to ask "Can the police search mycar when I'm not there?"

The only situation where the police would require your presence is if the justification for the search was your consent. Otherwise, the search could be based on the car appearing to be abandoned, unlawfully parked (which would permit it to be towed and inventoried), used in a crime, based on probable cause, incidental to an arrest, or other other circumstances. Even a consent search would be lawful if you or someone else having control of the vehicle had given their consent for a search with you not present.

A large number of cases fit this description, since the Supreme Court has taken an active role in defining the limits of Fourth Amendment protection against illegal search and seizure. The following are a selection of 4th Amendment precedents:

Michigan Department of State Police v. Sitz, 496 US 444 (1990) upheld the use of sobriety traffic checkpoints; however, Indianapolis v. Edmond, 531 US 32 (2001) held that this rule does not extend to checkpoints designed to search for drugs, because the search is too generalized. In Edmund, the search was confined to the use of drug-sniffing dogs (which is legal if the car is lawfully stopped) and outside visual check.

Florida v. Bostick, 501 US 429 (1991) held that evidence obtained during random bus searches, if conduct with the passengers' consent (even if the passenger feels compelled by circumstances to agree), is not a violation of the Fourth Amendment prohibition against unreasonable search and seizure.

Florida v. Royer, 460 US 491 (1983) held that police cannot hold someone without probable cause, and any evidence found during the detention is obtained illegally and may not be used as evidence, even if the person appears to agree to the search.

Oliver v. United States, 466 US 170 (1984) held that open fields are not protected by the Fourth Amendment, even if they are fenced and marked with no trespassing signs.

Minnesota v. Dickerson, 508 US 366 (1993) held that drugs detected by touch during a routine patdown can be used as evidence, but only if they were found in an area that might logically conceal a weapon.

Ohio v. Robinette, 519 US 33 (1996) held that a lawfully detained defendant does not need to be told explicitly that he or she is "free to go" before they can voluntarily agree to a search and seizure. Conviction on drug charges also upheld, despite defendant being stopped for another cause (speeding).

Illinois v. Caballes, 543 US 405 (2005) held that drug-sniffing dogs may be used during routine traffic stops (but not at checkpoints).

Bond v. United States, 529 US 334 (2000) held that a person has a legal expectation of privacy if their luggage is stored in a compartment (referring to a bus or other public transportation), and that any police manipulation of that luggage constitutes illegal search and seizure.

New York v. Belton, 453 US 454 (1981) held that police can search the passenger compartment of a stopped car and any containers found inside it as part of the valid arrest of any of the vehicle's occupants.

Pennsylvania v. LaBron, 518 US 938 (1993) held that police do not need to obtain a search warrant for a vehicle if the vehicle is capable of leaving the scene, even if there is time to obtain a search warrant.

Wyoming v. Houghton, 526 US 295 (1999) held that police can search a passenger's belongings inside a car if they already have probable cause to search the car.

Thornton v. United States, 541 US 615 (2004) held that police may search the passenger compartment of a suspect's car, even if their first contact with the person occurs after he or she leaves the car.

California v. Acevedo, 500 US 565 (1991) held that police can conduct a warrantless search of a paper bag in the trunk of a car if they have probable cause to believe the bag contains drugs.

California v. Carney, 471 US 386 (1985) held that police can conduct a warrantless search of a motor home (RV) if they have probable cause.

United States v. Villamonte-Marquez, 462 US 579 (1983) held that customs officials may conduct warrantless searches of boats pursuant to Title 19 USC §1581(a).

California v. Ciraolo, 476 US 207 (1986) held that police may take unaided aerial photographs of the area immediately surrounding a home using a private plane or helicopter as long as they are in public airspace.

Florida v. Riley, 488 US 445 (1989) held that police do not need a warrant to observe an individual's property from public airspace.

Arizona v. Gant, (slip opinion) (2008) held that police may search the passenger compartment of a vehicle incident to arrest, and without a warrant, only if it is reasonable to believe that the arrestee might access the vehicle at the time of the search, or if the vehicle contains evidence of the offense of arrest. (Compare with the decision in Belton; Gant narrows the exception).

Kyllo v. United States, 533 US 27 (2001) held that use of a thermal imaging device to detect grow lights being used inside a house for cultivating marijuana is a Fourth Amendment violation and requires a warrant.

Alabama v. White, 496 US 325 (1990) held that an anonymous tip as corroborated by independent investigation, is sufficient to provide reasonable suspicion to make an investigative stop.

Whren v. United States, 517 US 806 (1996) upheld the conviction on drug possession charges of two individuals who were pulled over because police became suspicious when they sat too long at a stoplight. Defendants claimed there was no probable cause to stop them. The Court ruled that the temporary detention of a motorist does not violate the Fourth Amendment prohibition against unreasonable seizure, "even if a reasonable officer would not have stopped the motorist absent some additional law enforcement objective."

Colorado v. Bertin, 479 US 367 (1987) held that contraband discovered in the process of inventorying an impounded car is lawful, and the items can be used as evidence in court.

Murray v. United States, 487 US 533 (1988) FDA agents observed suspicious activity occurring in and around a warehouse, with numerous vehicles driving into the warehouse and exiting a few minutes later. Two vehicles were stopped and the occupants were arrested for marijuana possession. After everyone left the warehouse, the DEA agents broke in, observed 270 bales of marijuana, then left to obtain a search warrant. They did not inform the magistrate of the break-in when requesting the warrant. The lower courts hed the warrant was invalid because the agents hadn't been forthcoming about entering the building prior to requesting the warrant. The Supreme Court reversed, holding the Fourth Amendment does not preclude admission of evidence discovered in an illegal, warrantless search if the same evidence is discovered later using a warrant.

New Jersey v. T.L.O., 469 US 325 (1985) held that public school searches do not require warrants as long as there is reasonable cause tot suspect illegal activity of the presence of contraband.

Illinois v. Gates, 462 US 213 (1983) overturned the landmark decisions in Aguilar v. Texas, (1964) and Spinelli v. United States, (1969), and replaced the Aguilar-Spinelli Test that gives little weight to confidential informant or anonymous tips when granting search warrants with a "totality of the circumstances" test.

United States v. Leon, 468 US 497 (1984) Established the "good faith" exception to the exclusionary rule that held evidence procured using defective warrants issued in error using insufficient probable clause could be used in court if the police had acted on the warrant in good faith (believed it was valid).

United States v. Santana, 427 US 38 (1976) held that a warrantless arrest inside the suspect's home was justified because the suspect was standing in a doorway when police approached. Since she was in full public view, she had no expectation of privacy. Retreating inside the house did not trigger Fourth Amendment protection because the arrest had been set in motion in a "public place."

Much of the case law permitting warrantless entry under exigent circumstances is determined by lower federal and state decisions, and is beyond the scope of discussion here, due to the level of expertise and detail involved in the explanation. The subject is discussed in detail in law enforcement training manuals.

Given the content and purpose of the Amendment, it would be something to do with an unreasonable search or seizure of property.

Amendment IV

The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
A search or seizure, The Fourth Amendment protects against a search or seizure

Police officers are mainly the people who have the right to search you and security guards also.

Added: The question is too generally worded to be answered in specifics - and the above answer is not entirely complete or correct.

Law enorcement officers are able to conduct pat-downs, frisks, and body searches only under certain proscribed circumstances as set forth in law and in decisions and guidelines laid down by the US Supreme Court.

For a more specific answer, the exact circumstances of the incident must be more clearly described.