Emmett Brown used a tape recorder as part of his automatic retrieval feature on the temporal duplicated DeLorean time machine. He left a message for Marty McFly letting him know that the appearance of the DeLorean without him in his timeline meant that Doc was in trouble at some point. He told Marty to go to the time coordinates listed on the "last time departed" entry on the time circuit panel.
In 1931, Marty used Doc's tape recorder to record Doc's younger counterpart struggling to answer an equation, so that the older Doc could solve it for him. He later used it to record Kid Tannen so that Tannen's accountant, Artie McFly, would be tricked to come out of hiding. This allowed Doc to serve him with a subpoena.
- Back to the Future: The Game
- Episode 1: "It's About Time" (First appearance)
- Back to the Future: Citizen Brown