I've always wanted to know how high my small low powered rockets would fly. Thanks to a company called "Winged Shadow Systems" this is now possible. The altimeter is called "How High SP" and is a small and lightweight device combining an altimeter and a battery board to create a completely self-contained, self-powered altitude measuring instrument. It only weighs 0.25 oz (7.2 grams) and that includes the batteries!
You can find more information about the altimeter at www.wingedshadow.com.