Eagle-eyed observers claim to have spotted Clinton, wearing what appears to be an hidden earpiece during the debate,Daily Mirror reports.
Footage from the 90-minute discussion at Hofstra University in New York also appears to show the outline of wires and a battery pack under Clinton's jacket.
Social media users were also quick to point out that Republican Trump was not wearing a similar device.Following criticism of his debate performance, Trump claimed he was given a "very bad" microphone and that debate moderator, Lester Holt of NBC News, asked him "very unfair questions".
"I don't want to believe in conspiracy theories, of course, but it was much lower than hers and it was crackling."In response, Clinton told reporters on her campaign plane: "Anyone who complains about the microphone is not having a good night."Fueling earlier conspiracy theories that Clinton is hiding a secret illness, some observers suggested the mystery box was related to her alleged ill-health.