Kindly check out the Drawdio project started by MIT media labs. A very little circuit which turns almost everything into an awesome theremin. Based on 555 timer IC, circuit is modified to use TI's low power version TLC551 which runs on a single AA or AAA battery. Enjoy and Share!

It advised to use TLC551 because transistor BC547 is biased for max 3V. If you want to use 555 then kindly recalculate all the components connected with BC547.