Legal Definition of pen register
: a device that registers the numbers dialed from a telephone — compare wiretap
Additional Notes on pen register
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.
Origin and Etymology of 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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