A search or seizure is reasonable when the police are acting on a warrant signed by a judge that specifically states what items or people are being sought, and where the authorities expect to find them. To obtain a warrant, therefore, the police must be able to present a minimum amount of proof – known as probable cause – to the judge. A search and seizure is a violation of privacy, so it must be justified.
People may waive their right to privacy by giving the police permission to enter their homes or to search their property. The police are trained in getting suspects to consent to searches because it’s easier than getting a warrant. There are other situations, known as exigent circumstances, where a search and seizure may be justified without a warrant or the suspect’s consent: