pen register

noun

pen reg·​is·​ter

: a device that registers the numbers dialed from a telephone compare wiretap

Note: A court order is always required for the use of a pen register in a criminal investigation, but such use has not been considered a search or interception of communication by the U.S. Supreme Court. Some states have disagreed and discern a privacy interest in such information.

Word History

Etymology

perhaps from the original use of a pen to mark the dots or dashes used in counting the numbers dialed