pen register

pen reg·is·ter

Legal Definition of pen register 

: 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.

History and Etymology for pen register

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

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not any or not one

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