These cameras are relatively new to the market. They are basically Wi-Fi video cameras which means they operate on a wireless WLAN network. This network enables wireless network communication over small areas by using infrared or radio transmitted signals instead of wired or cabled networks. The cameras are used primarily for security and surveillance purposes. You can place wireless cameras wherever you want to as long as they are in range of a WI-FI transmitter.
Most cameras are equipped with motion sensors and are capable of taking photographs, short videos and notifying you when there is movement near the camera. The cameras have their own built in server software and work more or less like a wireless laptop computer. Most of them don't have microphones though, so you can't hear any sound.
Some wireless models can automatically send you a photo by email if the camera detects movement. You can also get the emails sent to you on a regular basis. Some cameras come with software so you can watch through the camera's eyes on a computer. You should be able to find a wireless camera for under $200.
