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.
Step 2: Invisible laser alarm system
2 coin cell batteries (CR 2032/2025)
LDR (light dependent resistor)
Piezo or any other siren or buzzer
Strong IR LED
It is a very simple circuit. It is to be put on the gate. You will need to make two different circuits. Each at one side of the gate. One circuit is for sending the invisible light and the other is for receiving the light. Its just a simple IR LED which emits a light which humans cannot see and on the other side is a dark detecting circuit. When the person comes from the gate he will stop the light from being received and the alarm will sound up. The schematic for the dark detecting circuit and the installing scheme is given in this step.
Step 3: SHOCK protection system
Some metal rods (or the substitute I've given below)
A high voltage low ampere circuit
A battery for the circuit
The metal rods can be very expensive for you because this device needs many of them. So as a substitute you can make a cheaper one instead which is given in the next step.
Step 4: Substitute metal rods
Some foil paper
A little tape
First to make the base you should roll one large sheet of newspaper from the corner and keep rolling it as tightly as you can and once rolled seal it with some tape. Once the stick is made(as shown in the picture) just roll some foil paper on it and it should be ready.