High Quality Content by WIKIPEDIA articles! A hidden camera is a still or video camera used to film people without their knowledge. The camera is "hidden" because it is either not visible to the subject being filmed, or is disguised as another object. Hidden cameras have become popular for household surveillance, and can be built into common household objects such as smoke detectors, clock radios, motion detectors, ball caps, plants, and cellphones. Hidden cameras may also be used commercially or industrially as security cameras.