Someone had the time to make a laser marker sing Still Alive from Portal (not that there's anything wrong with that).
Keep watching! You'll realize something by the middle of the video. It seems that he uses lasers of different intensities to create different tones.
It took quite a while to get it this far. Laser markers weren't really meant for making music and there are a few parts out of time but I'm sure GLaDOS would approve.
GLaDOS would approve of course, she does like baking things.