My guess would be that the narrator has to be in a cell somewhere--either in a jail or in an asylum--and that he is not speaking aloud but is probably writing a sort of explanation or confession. The narrator seriously believes that he is perfectly sane. This is one of the unsettling features of Poe's story."The Tell-Tale Heart" ends with the murderer telling the visiting officers exactly where to find the body, so they would have to take him into custody and keep him locked up. I don't know if Poe invented this approach to writing a story, but I am reminded of Vladimir Nabokov's novel Lolita which is told by Humbert Humbert while he is being held in a prison cell after murdering Clare Quilty. Nabokov makes frequent references to Edgar Allan Poe throughout Lolita. The first-person narrative technique used in this story also resembles some of the dramatic monologues of Robert Browning (1812-1889), who may have been influenced by Poe directly or indirectly. I am also reminded of the narrative technique used by Albert Camus in The Stranger.