Cup Sensors for beer pong

Ok, I know it sounds a bit juvinile, but here's my idea. I want to build a beep pong table using the arduino to control multiple rgb led and some music sensitive led's. That's the easy part of which I have no problems doing, but here's where I need help. I would like to make the surface under the cup sensitive to their position(i.e.) green when the cups are in place, but red when they are taken off the table) any ideas on that? Any help is greatly appreciated.

Strong magnets on the bottom of cup... many "hall" sensors in the table?

Interesting idea I will research hall sensors. Thanks agin

I don't know if you've seen this (or if it was actually your post), but there is a good discussion of this exact topic over on the sparkfun forums

http://forum.sparkfun.com/viewtopic.php?t=14967&highlight=pong

The goal there though was to ensure the cups were unmodified - both from a "don't want to drink from a cup with electronics in it" and "don't want to affect the weight/dynamics of the cup" point of view

thanks you very much ;D

you could also check out sparkfun's reed switches if you wanted to go the magnetic route. If you want to just use unmodified dixie cups, I would check on something like sensitive switches people use for whiskers on robots. Something like this mounted into a pad http://www.sparkfun.com/commerce/product_info.php?products_id=98