Smith v. Maryland
Citation: 442 U.S. 735 (1979)
Facts
Police asked the phone company to install a pen register at its central office to record the numbers dialed from Smith’s home phone, without a warrant. Smith argued this was an unconstitutional search.
Issue
Does the installation of a pen register — which records numbers dialed but not the content of calls — constitute a search under the Fourth Amendment?
Holding
No. Smith had no reasonable expectation of privacy in the numbers he dialed because he voluntarily conveyed that information to the phone company, which could record it. Using the phone company’s equipment to collect the data the company already had access to is not a search.
Rule
Third-party doctrine (pen registers): When a person voluntarily conveys information to a third party — here, the phone company — they assume the risk that the third party will turn that information over to the government. Numbers dialed are conveyed to the telephone company as a matter of course; there is no Fourth Amendment protection in that information.
Significance
- Classic application of the third-party doctrine to telephone records
- Companion case to United States v. Miller (bank records also unprotected under third-party doctrine)
- Carpenter v. United States (2018) limited the doctrine: cell-site location information, despite being held by a third party, receives Fourth Amendment protection because of the volume and comprehensiveness of the data
- The Smith rule still applies to pen registers and call records (not content); Carpenter is the modern limit