ok this is the most i would go to, get some duckt tape or sumfink tape the tope of a sheet abve your window and along the sides so you can get underneath it and put ur head out the window and smoke the smoke wont come back in cause of the ssheet and if you hear your mum just rip the sheet of chuck the joint out the window if your on the ground floor or just leave it on the windowseal and tell your mum you felt a bit sick so you was getting some fresh air , i recomend smoking a joint instead or anythink else as you can drp it wivout your weed coming out n its easy to hide