The market offers different types of hidden cameras that will surely meet the need of every individual. However, due to a variety of choices people are confused on which device is the most suitable for their security needs. After my extensive research, I learn three types of commonly used hidden cameras.
Wireless (hidden) cameras which transmit video: These cameras are quickly becoming obsolete because they need to transmit the video over the air, thus requiring the end user to be within range of the transmitter (usually within 100 yards) in order to receive the signal.
Wired cameras: Wired cameras (hidden or not) or just that-they require a wire to send the video down, as well as power (either battery or AC).
Wireless cameras that store video locally: These cameras are by far becoming the superior product of choice. They could be built into a clock/radio alarm and use the power from the AC power cord (which also powers the clock), or they could be found in bird houses or discrete black boxes without any cords (and thus run on battery power).
If you want additional information about different types of hidden cameras, you can make research or seek an advice from professionals and experts. Buy hidden cameras to protect yourself and your belongings.
source: http://ezinearticles.com/?How-to-Find-a-Hidden-Camera&id=2965224