if you have a smoke detector that looks like this (like i do in my room);
then it is not a smoke detector, it is a heat detector.
when you are smoking in the room, the main issue is not the actual smoke, its the smell. i know, we had the cops called on us a few weeks ago, $200 fine, but whatever. fuck the police.
get a fan blowing out the window and another if you have one in front of the door. with these two fans, it will still probably smell like weed a little in your room, but the second fan will stop the smell from going past the door (how i got caught... + the noise of 20 people). spray some fabreeze and you are fine.