ThinkGeek is now featuring this very geeky t-shirt that changes based on the strength of wi-fi signals being detected. Since I looked up whether the short would detect only open wi-fi signals (not that it says), I think that says I am pretty geeky. An insight into how this works is provided by the washing instructions:

Washing Instructions

Carefully peel animated decal from front of T-Shirt

Unplug ribbon connector behind decal and remove decal

Unplug battery pack and remove it

You can leave the ribbon cable inside the shirt

Machine wash gentle cycle on cold

Hang to dry