My roommate is a very considerate person, yet he has a habit of leaving our room door open when he goes to the common room. To be frank, I don’t mind open doors in the daytime. But since I am a light sleeper and get awaken by the slightest rise in light or sound intensity, my roommate’s trips to the common area in the nighttime disrupt my sleep. This is why my first class assignment for Intro to IM features a switch that turns on the LED when the door gets open.