When it is difficult to run a cable to transmit video signals of the camera to the monitor, you might want to consider wireless transmission. But, the wireless signals may be attenuated or blocked by heavy metal walls, high voltage power lines, microwave equipment and others.

The wireless system is strictly controlled by the FCC. The commercialized models are usually FCC approved by the manufacturers and you don't need to get a separate FCC approval. But, you can not change or modify the specification of each model without prior approval from the FCC. Each manufacturer has different bandwidths of frequency approved from the FCC and will not be compatible with other manufacturer's models.

Most commercialized wireless systems have 4 or 10 channels; you can not use more than 4 or 10 transmitters in one area due to conflicts of the overlapped channel(s). But you can have as many additional wireless receivers as you want as far as they are within the range.