Need room security! please! Answered

One thing maybe have your dad build a door frame? so you can get a padlock on the outside?

Buy a Goose. They are load, territorial, and make great watch dogs.

Maybe set a carpet across the entrance that has a on\off push switch underneath which is connected to a infrared emitter (radio shack), that is turned on and sends a signal to a infrared detector (radio shack) which goes through another switch, which only you can reach or figure out how to turn off or something like that, to a piezo alarm. Or just directly connect the on\off switch to the piezo, but i'm pretty sure your siblings would figure out that all they would have to do is step on the mat again to turn it off :)

THANKS I THINK I MIGHT TRY (oops srry bout the caps i accidently hit the button) some of those

Just hang a beaded curtain and attach small bells etc.

one other idea, check at a local electronics store, if they have this sound grenade thing, get it, you can easily mod it, mount it on a wall, and run fishing line across the door, it has a pull pin, and is really cheap.

Like XOIIO mentioned, buzzers are fun. I would use one of those annoying mcdonald toys that when pressed or shaken makes a sound. Attach it to the door with some wire, aluminum foil, and sticky tape.

Try hooking up some stickytape sensors to the floor and abuzzer! Or check for a window/door alarm at the dollar store!