A nanny cam, or nanny camera, sensationalised to the phrase "spy camera", is a hidden video camera that has been secretly installed within a common household object and is usually used to secretly monitor and record the activities of home caregivers, such as nannies, hence the name, although it has its usefulness to overtly or covertly record any activity.
Function and usage
The receiver can be connected to a video recorder (VCR) or DVR recording device or can be a portable receiver-screen which can be carried room to room by parents to keep an eye on their children. The camera can be hooked up to an Internet broadband connection for remote viewing while at work or vacation, in which case it is also a webcam. 
It can be connected to a VCR or DVR, either with:
Some nanny cameras are self-recording camcorders that record the video internally to a hard drive or memory card, which eliminates the need for a wireless receiver or wired connection to a VCR or DVR.
There have been many news stories centered around a hidden camera that has recorded a nanny in the act of abusing a child. Nanny cameras can also be used to prove the guilt or innocence of a suspected abuser.
For convenience, most nanny cams use built-in transmitters to send their video to a recording device located in another room or floor.
||The examples and perspective in this section deal primarily with USA and do not represent a worldwide view of the subject. (December 2011)|
US Code Title 18, Chapter 119, Section 2512 prohibits the interception of oral communication by "surreptitious manner" such as a hidden camera, and so most nanny cams are not available with audio recording. Though some on the market may be available with the ability to record audio, these cameras should not be used due to the illegality of the recordings they produce. Nanny cams are legal in all 50 states, but it is illegal in 13 states to record audio without express or written consent of the nanny being recorded. This falls under the federal government's 'wire tapping' laws.