As a child I was fascinated by the “eye in the back of her head” my mother  claimed to have. I never found it, but then she did have long hair.

The technological equivalent of that “eye” is a video surveillance camera, or network video-cam. While some are designed for surreptitious surveillance of, say, the nanny, most are designed as stand­alone home or small business security equipment, or as part of a home security package.