Nanny cams usually refer to covert cameras. The basic principle is to have hidden cameras that can record events that occur while a nanny or caregiver is caring for someone. Hidden cameras are available in many forms. Unfortunately, you will often sacrifice quality with many of the usable hidden cameras. The most common covert cameras are smoke detector and motion detector cameras. Smoke detectors are often found in many rooms in the common household. Covert smoke detector cameras look just like the real thing, only they have a small board camera hidden inside. They make great nanny cams because they almost never look out of place. The next most common nanny camera is the covert motion detector. If you have an alarm system in your home, then a spy camera installed inside of a common alarm system motion detector will not look out of place. As an added bonus, some actually work and detect motion and flash just like the real thing.
Both of these cameras are excellent choices for spy cameras or nanny cams. They are usually connected to your DVR just like any other camera.