i was just doing some reading in here and I came across your post. I have alink for you. it is a toy that can be hacked to suit your needs. one main problem with it is it's reliability. but it might ave you some time and money. i modified the reciver board to communicate with a pic. The receiver board is a lot smaller then the big plastic toy housing, so it will fit in a much smaller box. the sensors/transmitter are smaller then hockey pucks and have decent range. maybe 20-30 meters
have fun.

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