Wireless spy cameras have many of the same features of a wired camera system and there are many models, offering various features.
A Wireless Camera is a combination of a Camera and a radio transmitter/receiver.
Because it is a radio transmitter/receiver, you will have a few issues not present when using a standalone or wired spy camera system. The main issues will be how much range the camera system will get, how many wireless cameras can be used in one location, the quality of the video signal and if the video feed is secure.
The range is the distance from the camera transmitter to the receiver. The video quality can be affected by the distance, Analog transmitter/receivers send video signals over the open airways, where interference can be applied by other devices (cordless phones, baby monitors, radio scanners). Digital transmitter/receivers are encrypted provide increased privacy and allow for more cameras per location.