Here is a movie of what happens and what it sounds like. I'm going to probably post one with the trip wire in real action but for now, enjoy!
An alarm featuring a small electric motor that produces a high pitched whine
Step 1: Gather yer parts
To make a long story short my dog chewed up this plastic helicopter that went to this clever toy my dad brought home from some company at work. At any rate this toy featured an adjustable base wth a one of those DC electric motors inside. The motor in turn turned the helicopers rotor and when the switch was released, made the copter fly into the air. A any rate that's what I used to make the obnoxious alarm sound (ie: the copper coils and magnets grinding together in the motor). If you have this toy and coinicidentally you have the same predicament as I did, assemble your alarm as shown. If not, a sturdy piece of card board with a DC motor taped on top should suffice. Along with that you'll need two double A batteries, some wire if you are not making yours out of the the heli copter toy, kite string, duct tape, a glue gun, and a 50 cent D-CON mouse trap.