candid camera

noun2

1. •
   A camera which is concealed or unobtrusive, used to obtain candid photographs of people who usually are unaware; the practice of taking such photos.

   • A candid camera’s role in higher education, with photographs of co-eds in the nude, commanded public interest today. — 1937
2. •
   A humorous television show that uses hidden candid cameras to make jokes to people.