Don't do what Gaara said. Not only is it unnecessary, but it can actually get you in trouble -- I don't know if you're on campus property or not, but at least on most campuses you are not allowed to tamper with fire alarms. Same probably goes for many apartment complexes. Disabling or tampering with the alarms usually sends out a signal to your local safety HQ or whatever. Many of my friends have done this, only to wind up with campus safety at their door a few hours later. If you put the fan in your window properly, it's actually a good idea NOT to towel the door. If you're trying to move air out of your room, you need to be able to let fresh air into your room, right? As long as the fan is blowing air OUT of your room, you don't have to worry about air creeping out into the hallway from underneath your door. To test your ventilation, crack your door a little bit and turn on the fan -- the door should be pulled inwards from the negative pressure created by the fan. Also, feel around the cracks of your closed door when you've got the fan on -- you should feel a draft coming into your room from between the cracks. That's when you know you've got good ventilation