Physical interaction design DH2400

A nice idea about "coloring" the city :)
With really simple materials (led lights, batteries, magnets and strapping tape) and with low cost (ebay ftw) everyone can create small, colorful "objects" that can be attached to anything metallic and stay there for almost 2 weeks.

More info here, here (check the extra links below the video) and here.

Just to get a small taste :

http://www.youtube.com/watch?v=4fbAEejVK0w
http://www.youtube.com/watch?v=TrnLF04qmsM

Now, imagine use something that simple and extend it with interaction functionality. How about making the leds active on the presence on someone in front of them? Or maybe only at night? Or perhaps make them turn on and off based on the level of the surrounding sound?

I know that every possible extended idea would need extra modifications, but I think that color and simplicity is what is missing in our time :)