Do you want your annoying pets to stay away from your room at night?
Step 1: Materials
All you need is one of those staple-taker-outers that look like mouths, some fishing string/wire, 2 rubber bands, some kind of inch-long half-centimeter-wide tube, and some duct tape.
Step 2: Assembly 1
Wrap 1 rubber band around the staple-taker-outer loosely so that it isn't stuck shut. You need to be able to move it easily. It needs to want to shut though.
Step 3: Assembly 2
Now tape the staple-taker-outer sideways to the wall a few inches off the ground.
Step 4: Assembly 3
Now tie the rubber band around the tube as shown in the picture below.
Step 5: Assembly 4
Now put the tube in the teeth of the staple-taker-outer. Not all the way in, but just so the teeth are holding it. You should easily be able to pull it out.
Step 6: Assembly 5
Now tie the fishing wire to the rubber band tightly. Don't cut the fishing wire yet.
Step 7: Assembly 6
Now tape the other end of the fishing wire to the other side of the doorway. Cut the fishing wire. You should have what looks like a trip wire across the doorway. When your cat/dog tries to walk into your room, they will trip on the wire, sending the tube out of the staple-taker-outer's mouth. The tube will gently strike your pet's side. Your pet will be stunned and run out of your room. If the tube doesn't launch out of the staple-taker-outer's mouth, tighten your fishing wire, and try it again.