At Barcamp Liverpool last weekend I gave a talk about getting started with Arduino, and showed how to hack a toy ray-gun so it would flash its lights and make noises when anyone mentioned Barcamp Liverpool on twitter.
As I had a spare Arduino BT lying around, I also built Bubblino. An app on the laptop monitored twitter for people mentioning the conference, and when it spotted any it would connect to Bubblino via Bluetooth and tell him how many mentions there'd been.
Bubblino then blew bubbles to show attendees that they were being talked about - more mentions meant more bubbles 
I've stuck a video of him in action, and written up a bit about him over on the Bubblino homepage.