I watch a lot of Law & Order, so I did a little research, and a bell dinged in my head. You don't always need a search warrant.
Police officers do not need a warrant to make a search "incident to an arrest." After an arrest, police officers have the right to protect themselves by searching for weapons and to protect the legal case against the suspect by searching for evidence that the suspect might try to destroy. Assuming that the officer has probable cause to make the arrest in the first place, a search of the person and the person's surroundings following the arrest is valid, and any evidence uncovered is admissible at trial.
To justify a search as incident to an arrest, a spatial relationship must exist between the arrest and the search. The general rule is that after arrest the police may search a defendant and the area within a defendant's immediate control. For example, an arresting officer may search not only a suspect's clothes, but also the suspect's wallet or purse. If an arrest takes place in a kitchen, the arresting officer can probably search the kitchen, but not the rest of the house. If an arrest takes place outside a house, the arresting officer cannot search the house at all. To conduct a search broader in scope than a defendant and the area within the defendant's immediate control, an officer would have to obtain a warrant. However, the police may make what's known as a "protective sweep" following an arrest. When making a protective sweep, police officers can walk through a residence and make a "cursory visual inspection" of places where an accomplice might be hiding. For example, police officers could look under beds and inside closets. To justify making a protective sweep, police officers must have a reasonable belief that a dangerous accomplice might be hiding inside a residence. If a sweep is lawful, the police can lawfully seize contraband or evidence of crime that is in plain view.
There are other instances of when you don't need a search warrant, so I'll post the link where I found it all.
http://www.nolo.com/lawcenter/ency/article.cfm/objectID/50CD91FC-B21D-4BE7-BA4818C8E29AC758 Ciao
Jen
