Generally, officers may obtain a valid consent to search only from a person whose reasonable expectation of privacy may be invaded by the proposed search. Sometimes two or more people—for example, spouses or roommates—share a reasonable expectation of privacy in the same place. Generally, either person may give valid consent to an officer. United States v. Matlock, 415 U.S. 164 (1974) (common authority over premises found). However, as discussed below, an exception to this general rule may exist when a physically-present occupant objects.