Amazing... it's been a while since I've read an Instructable and immediately gone to make it. Took about ten minutes from scrounging parts to it working! Possible discovery for people wanting to tune them- my straw is a slightly loose fit so needs holding against the diaphragm to sound properly, and the note can be adjusted a little by changing the force with which it is pushed against the diaphragm. Has anyone considered adding another tube to the "in" hole and using another (whole) balloon as a low-tech air supply? Could be fillod by blowing through it backwards, and the possibilities for adding a solenoid valve and using it as an alarm clock are frankly worrying...