A homemade instrument that you can change the pitch of?

I have a project for science that consist of me making a instrument that can show a variety of pitches. I can't make a guitar out of a hollow object, because it has to be more elaborate. And I cannot set up a variety of bottles and blow into them, because it has to be portable. If you could give me a link or possibly tell me how to make it that would be helpful.
Thanks~
Andrea ♥