Teleprompter

Hardware prompters reflect a screen off angled glass straight down the barrel of the lens, so your eyes land exactly where the camera is. App versions run on a phone or tablet propped as close to the lens as you can manage, and that distance is what gives people away: looking into the lens reads to a viewer as eye contact, looking a few inches off it reads as somebody reading. Pace is the other tell, since a prompter scrolls at one constant speed and human speech does not.