what does this do ? do yours have it ?

[Mister_Me]

hello, i just got a s15 and it has this button on the side of the steering wheel that i would like to know what it is and what it does.
when i flip it the light turns on and i have to flip it again for it to turn of. (sorry if this is the wrong section)
sorry for the bad quality image :

 

[pegliobaglio]

Heated screen mate. Will have heater wires around the edge of the front screen , apparently it is to free up the wiper blades if it freezes over