I plan to take a 555, wire it up into astable operation to make a square wave, and hook the output up to a transducer. It's Panasonic's 24C411, with a rated voltage of 15V peak-to-peak and a maximum current of 2mA. Apparently, the maximum output current of the 555 is 200mA, and a 9V can put out between 100mA and 200mA at the highest. I'd like to simply use a resistor, but would that just draw too much of the voltage? On the other hand, perhaps it would be better to use a speaker. I just remembered that I have a small one lying around.