Getting up in the middle of the night and flicking on a bright overhead light in the bathroom so you can use it isn't the best way to wake up. To solve that problem, 43oh forum member Fred decided to make a simple motion-sensitive light for his bathroom.
Using a LED light, motion sensor, MSP430-PIR board and a 9V battery, he was able to create a low-intensity light that provided enough brightness to help him get around, but not so much that his night-vision was disturbed. It's a clever little trick for anyone who has ever turned on a bright bathroom light in the middle of the night and then had trouble getting back to sleep afterward. Find the full guide and code over on the 43oh forums.