Here is my student Emma Jane who has just got her protoype e-bracelet working. It's designed to encourage teenage girls to learn to program. The bracelet (or arm band!) can be programmed to display secret messages in the form of lights or buzzers. Use case: you see a hot guy in the lunch queue. You move your arm in a particular gesture, or press a switch on your bracelet and it sends a message to your friend's bracelet where is displayed as a coloured light flash. Only you and your friend know what input on your bracelet maps to the output on yours. The components are Lilypad arduinos and XBees for the comms with accelerometers , lights, switches etc.