I once built an NXT robot that opened and closed a set of blinds.
The blinds had a rod that you could spin to open and close them, and the rod had a hole at the end, which made it pretty easy to hook up to a mindstorms motor.
I made two different versions. One version was a "clapper" - with a microphone sensor, and one was a smarter version, that used a light sensor. The light sensor was positioned on the outside of the blinds. When the sun came up, it would open the blinds, and when the sun went down, it would close them.
I could have combined them together - in fact, I was planning to do that - but then I decided to use the NXT unit for some other projects instead.