This is the first time I've heard of a pen register, apparently somewhat broad, modern parlance for things that capture phone data. It seems pretty damning that they spent the time to fax MetroPCS but couldn't, ya know, even get the pen register or ask a judge to ask if they thought it was a good idea. Maybe the bad guys are really bad, but sometimes I hope that they get off just to make the point that the cops are s…
The term dates back to 19th-century telegraphy [1]. 18 U.S. Code § 3127 [2] defines them specifically:
the term “pen register” means a device or process which records or decodes
dialing, routing, addressing, or signaling information transmitted by an
instrument or facility from which a wire or electronic communication is
transmitted, provided, however, that such information shall not include the
contents of any communication, but such term does not include any device or
process used by a provider or customer of a wire or electronic communication
service for billing, or recording as an incident to billing, for
communications services provided by such provider or any device or process
used by a provider or customer of a wire communication service for cost
accounting or other like purposes in the ordinary course of its business;