Where is the g4 ibook/powerbook sleep sensor?

I was wondering how/where the sensor is/works to tell the computer to go to sleep when the lid is closed. I am doing some mods (discussed in the marketplace forum) and would like to try to keep that sensor intact if at all possible, but i realized I have no idea where it is located or how it senses that the lid is closed on these.

Anyhelp would be great. I searched the forum a bit and found nothing, and can't find anything in google other then sleeping problems... unless I just am horrible at googlin

thanks in advance!

you are awesome! thanks!