On Mon, 22 Sep 1997 20:03:56 -0400 Pioneer Microsystems writes: >Just a thought, which I am yanking out of the muck of my memory... I >seem to >recall that ceramic disc capacitors can make a super cheap vibration >sensor. I >think it was for bearing monitors or something. If you just need a motion detector, not a precise accelerometor, investigate devices with moving mechanical contacts or conductive fluids. One having a spring of the proper stiffness could respond by closing a contact when the acceleration is more than its threshold value. Also, you might craft >a > resonant >sound chamber in the molding of the housing of the product for the >piezo souning >disc. Usually the resonant chamber is the diameter of the disk (with the disk forming the back wall), about 1/4 - 1/2" deep, and having a relatively small opening in the front wall for sound to come out. Look at a few products such as the Sonalert(tm) and Sound Bomb(tm). The depth of the sound chamber affects the optimum frequency. To make the sound as loud as possible you also need to drive the disk with near it's peak rated voltage, which is often 30V or more. This generally means a transformer or inductor to boost the voltage.