A Buzzer
You can make a buzzer that actually works. How loud would it be and what does it look like, depends on your creativity and plans. It involves some metal works and an electromagnet that you can simply make using a battery, some insulated copper wire and a steel peen or nail.
Your display can include a drawing of a buzzer with a working model that works and everyone can test.
 Material and step by step instructions
In this project you will make a working model of a buzzer and learn how a buzzer works. Most Electromagnet kits have the necessary material and step by step instructions on how to make a buzzer. Depending on how complete your kit is, you may need to purchase or gather some additional items to complete your project. 
 Details of this project
Support or more details on this project is available for the members of ScienceProject.com web site. Material or a science kit for this project may be available at MiniScience.com.