What tells the MacBook to sleep when you shut the screen?

[iBook_Clamshell]

Is there a mechanical switch in the hinge of the MB that tells the system when to sleep? Or is it in the magnets?
I have a 2006 13".

 

[logana]

There is a reed switch in the top of the battery connector (in the bottom left hand corner of the logicboard) that is tripped by the magnet halfway down the lefthand side of the lcd screen frame.....

 

[iBook_Clamshell]

There is a reed switch in the top of the battery connector (in the bottom left hand corner of the logicboard) that is tripped by the magnet halfway down the lefthand side of the lcd screen frame.....

Thank you very much!!!

 

[MCAsan]

Laptop gnome.