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There is a Hardy Boys book in which one of the boys makes a phone call to family with some nefarious person present. He holds an innocent conversation while sending a message in Morse code by tapping the phone with a pencil.

Based on an actual event from the Vietnam war iirc.

https://en.wikipedia.org/wiki/Jeremiah_Denton

In the 21st century this would be:

kidnapped by terrorists and forced to read a statement.

IIRC this was used in Homeland, the TV show.