Step 1 and 2- How to detect the people that are trying to get into your room.
Step 3, 4 and 5-How to stop people from entering your room.
Step 6 and 7- Help for step 5
Step 1: Tripwire alarm
9v battery and clip
Piezo or any siren or any kind of buzzer
A plastic peg/clip
Some thick thread and a piece of plastic
This is someone else's idea and is also available as another instructable
Its just a simple circuit and instead of the switch we'll use the clip. On both the points of the clip we'll use some duct tape or foil paper to attach the wire. Now if we leave the clip it will conduct if if we press it from the other side it will stop the circuit. We will simply take a peice of plastic or any other non conductive thing and tie a thick thread to it. Now tie the other end to some where on the other side and put the plastic peice in the clip to stop the circuit. When the person comes, the thick thread will get pulled and the plastic will get removed and thus, the piezo siren will start up.The schematic and a photo of the alarm made is given in this step.