[xone]

Then in Barr’s letter you have the announcement there were 50 pen registers (which is a different way of saying wiretaps)

Pen registers just get the number, not the audio.

[BiggBob]

That was pre 9-11 and Patriot act
Modern pen registers gather much more than just the phone number,
Including text message and email metadata. But technically the pen register does not record the phone call conversation. However getting the pen register would allow for probable cause to then get a ‘wiretap’ to listen to the contents of calls of numbers being called to/from by having the pen register.