The galaxy audio as-1100-4 is a wireless personal monitor which I understand allows you to hear the monitors as you perform while still allowing you to move around freely. This is especially important when playing live and for everyone in the band, not just the vocalist. I also understand that you need some sort of certification to operate it correctly, though you can still use it without one.
It has been nearly 10 years since I played live, so I could be wrong about some of these details. If you are interested in a wireless monitor system, take a moment to follow the link and check out the product for yourself.