Wireless hidden cameras, such as these, have both a camera and transmitter built inside of the object.
The object may be one of any number of things – mantle clock, alarm clock, toolbox, voltage box, exit sign, etc.
Inside of the object is both a camera and a wireless video transmitter. Also included with your purchase is a wireless video receiver. The receiver has a standard RCA jack on it for video output.
This video output jack connects to your TV video input or an input on your Security DVR. The transmission of video without wires is what makes a hidden camera wireless.