The purpose of obtaining a warrant is to have a neutral person who is not involved in law enforcement evaluate the justification to determine whether there is probable cause for action that police wish to take. In Johnson v. United States (1948), the Supreme Court elaborated on this sentiment:
The point of the Fourth Amendment, which often is not grasped by zealous officers, is not that it denies law enforcement the support of the usual inferences which reasonable men draw from evidence. Its protection consists in requiring that those inferences be drawn by a neutral and detached magistrate instead of being judged by the officer engaged in the often competitive enterprise of ferreting out crime. The importance of such a neutral evaluation is understandable given the fact that, out of necessity, warrants are issued ex parte (the only party before the issuing person is the state). If this were not the case, the target of the search would receive advance warning and could take action to frustrate the search.
There are two types of warrants, arrest warrants and search warrants, although arrest warrants are rarely used or required. Although search warrants are often used, especially in cases where there is an extensive investigation, the Court has broadened the circumstances under which the police may conduct warrantless searches. This will be the topic of the analysis on exceptions to the warrant requirement. Unlike arrest warrants, however, search warrants can grow stale with the passage of time. This consideration is reflected in the Federal Rules of Criminal Procedure 41(c), which states, “It shall command the officer to search, within a specified period of time not to exceed 10 days….”
It should be noted that it is possible to waive the warrant requirement for a search or arrest. In United States v. Knights (2001), a suspect had agreed, as a condition of his probation, that he would submit to a search at any time, with or without a search, arrest warrant, or reasonable cause. During his probation,