hidden camera (for illicit purposes)
Specifically a camera used for voyeuristic or illegal recording, such as upskirt photos or secret filming in private spaces. The term carries a strong negative connotation.
See also: 盗撮
A hidden camera was found on the station escalator.
Crimes using hidden cameras are increasing.
Compound of 盗撮 (とうさつ, 'voyeuristic filming') and カメラ ('camera').