The police can perform a search without a warrant in Pennsylvania in certain limited instances. Although the fourth amendment of the United States constitution prohibits unreasonable searches and seizures, which means in part that a warrant is generally required. There are certain limited instances where the police would not need a warrant to perform a search in Pennsylvania, namely, if a person gives consent to the search, or if the evidence or contraband is within plain view, or if it's a search incident to arrest, meaning that, say, the person is being arrested and the police perform a search accordingly, or, say, like a protective sweep, when the police are arresting a person, or if there's exigent circumstances such as a person flees into a house, or other circumstances of, say, like an emergent nature.
There are certain limited instances where the police can perform a search without a warrant in Pennsylvania. Having an experienced Pennsylvania criminal defense attorney in your corner, from as early as possible in the process, will help you best protect and maximize your rights.